ABRHS P AME Chapter 5: Newton’s Second La · Chapter 5: Newton’s Second Law 2015-16 ... A...

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ABRHS PHYSICS (CP) NAME: ____________________ Chapter 5: Newton’s Second Law 2015-16 Text: Chapter 5 Think and Explain: 1-5 Think and Solve: 1-6 Vocabulary: net force, inversely proportional, Newton’s 2nd law, normal force, mass, weight, friction, tension, system, pulley Equations: ma F net = F F net Σ = F g = mg F x = F cosθ F y = F sinθ Constants: g = ±10 m/s 2 1 kg = 1000 grams Key Objectives: Concepts Explain and apply Newton's Second Law of Motion. Understand the affect of applied force, friction, and net force on an object’s acceleration. Sketch free body diagrams for objects undergoing horizontal acceleration. Sketch free body diagrams for objects undergoing vertical acceleration. Understand the cart/pulley/mass system. (Newton’s Second Law Lab) Define friction and describe what it does. Problem Solving Use constant acceleration equations to solve for the acceleration of an object. Find the net force acting on an object given all of the individual forces. Use Newton’s 2nd Law to solve for the unknown value. Solve cart/pulley/mass problems.

Transcript of ABRHS P AME Chapter 5: Newton’s Second La · Chapter 5: Newton’s Second Law 2015-16 ... A...

Page 1: ABRHS P AME Chapter 5: Newton’s Second La · Chapter 5: Newton’s Second Law 2015-16 ... A dragster starts from rest and has a constant acceleration of 7 m ... A bicyclist traveling

ABRHS PHYSICS (CP) NAME: ____________________ Chapter 5: Newton’s Second Law

2015-16

Text: Chapter 5 Think and Explain: 1-5 Think and Solve: 1-6 Vocabulary: net force, inversely proportional, Newton’s 2nd law, normal force, mass, weight, friction, tension, system, pulley Equations:

maFnet = FFnet Σ= Fg = mg Fx = F cosθ Fy = F sinθ Constants: g = ±10 m/s2 1 kg = 1000 grams Key Objectives: Concepts Explain and apply Newton's Second Law of Motion. Understand the affect of applied force, friction, and net force on an object’s acceleration. Sketch free body diagrams for objects undergoing horizontal acceleration. Sketch free body diagrams for objects undergoing vertical acceleration. Understand the cart/pulley/mass system. (Newton’s Second Law Lab) Define friction and describe what it does. Problem Solving Use constant acceleration equations to solve for the acceleration of an object. Find the net force acting on an object given all of the individual forces. Use Newton’s 2nd Law to solve for the unknown value. Solve cart/pulley/mass problems.

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ABRHS PHYSICS (CP) NAME: ________________ Acceleration Problems Review Sheet

side 1

1. A car constantly accelerates from rest, covering 150 meters in 10 seconds. a. What was its average speed for this interval? b. What was its final speed? c. What was its acceleration?

2. Starting from rest, a rocket has a constant acceleration of 15 m/s2 for 30 seconds.

a. What is its final speed? b. What was its average speed over this time? c. How far did it travel?

3. A friend is rolling down a hill on a skateboard. Starting from rest, they roll to a final

speed of 12 m/s in 4 seconds. a. What was the average speed of your friend? b. What was the acceleration of your friend? c. How far did your friend travel?

4. A car accelerates from rest to a speed of 30 m/s in a distance of 250 m.

a. What was the average speed of the car? b. How long did this take? c. What was the acceleration of the car?

5. A sprinter accelerates from rest and covers 5 meters in only 2 seconds.

a. What was the average speed for this interval? b. What was the final speed? c. What was the acceleration?

6. A dragster starts from rest and has a constant acceleration of 7 m/s2 for 8 seconds.

a. What is its final speed? b. What was its average speed over this time? c. How far did it travel?

7. Starting from rest, a plane accelerates to a final speed of 100 m/s in 25 seconds.

a. What was the average speed of the plane? b. What was the acceleration of the plane? c. How far did the plane travel?

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ABRHS PHYSICS (CP) NAME: ________________ Acceleration Problems Review Sheet

side 2

8. A car accelerates from 20 m/s to 35 m/s in a time of 10 seconds. a. What was the average speed of the car? b. What was the acceleration of the car? c. How far did the car travel?

9. Another car slows down from a speed of 32 m/s to a speed of 8 m/s in a time of 12 seconds.

a. What was the average speed of the car? b. What was the acceleration of the car? c. How far did the car travel?

10. A bicyclist traveling at 20 m/s stops in a distance of 120 meters.

a. What was the average speed of the bicyclist? b. How many seconds did this take? c. What was the acceleration of the bicyclist?

11. A ball has some initial speed. It slows down and comes to a stop in a distance of 23

meters and a time of 6 seconds. a. What was the average speed of the ball? b. What was the initial speed of the ball? c. What was the acceleration of the ball?

Answers: 1. a) 15 m/s b) 30 m/s c) 3 m/s2 2. a) 450 m/s b) 225 m/s c) 6750 m 3. a) 6 m/s b) 3 m/s2 c) 24 m 4. a) 15 m/s b) 16.7 s c) 1.8 m/s2 5. a) 2.5 m/s b) 5 m/s c) 2.5 m/s2 6. a) 56 m/s b) 28 m/s c) 224 m 7. a) 50 m/s b) 4 m/s2 c) 1250 m 8. a) 27.5 m/s b) 1.5 m/s2 c) 275 m 9. a) 20 m/s b) –2 m/s2 c) 240 m 10.a) 10 m/s b) 12 s c) –1.67 m/s2 11.a) 3.83 m/s b) 7.67 m/s c) –1.28 m/s2

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ABRHS PHYSICS (CP) NAME: _________________

Lab 5-2: Newton's Second Law

side 1

Purpose: To determine an equation that describes the relationship between acceleration and applied force for an object of constant mass.

Materials: 1 (one) 200 gram slotted mass 1 (one) 100 gram slotted mass 1 (one) 50 gram slotted mass 2 black bars (500 grams each) 1 string (~75 cm) 1 pulley 1 hanger (50 grams) 1 cart (500 grams) Procedure:

1. Set up the track, cart, pulley, hanger and motion detector as shown in the diagram below.

lab table

empty hanger (1st trial)

2 bars & all slotted masses> 20 cm

2. Record the mass of the cart, string and hanger on the other side of this sheet. 3. Make sure the track is level. The cart should not be rolling in either direction. Also, make

sure that the string is attached to the pulley horizontally. (This means the string is over the end bar of the track.)

4. Start LoggerPro. Open up the file “02 Cart.cmbl”. Make sure the bottom graph is velocity vs. time.

5. Put the cart on the track. Place the two extra 500 gram masses on the cart. Place all the slotted masses on the cart. Secure the slotted masses with some masking tape. (Just enough so that the masses stay in place.)

6. Pull the cart back and hold it. Make sure that there is at least 20 cm between the cart and the motion detector. Start collecting data. When you hear the motion detector, release the cart. Don’t let the cart slam into the end of the track!

7. To determine the acceleration of the cart, measure the slope of the best fit line of the velocity graph. You will have to highlight the portion of the graph that shows the cart speeding up.

8. Repeat steps 6 and 7 above for seven more trials. For each new trial, transfer 50 grams from the cart to the hanger and measure the resulting acceleration. (If there are only 100 gram masses on the cart, switch a 100 gram from the cart with the 50 gram on the hanger.) Do not add any new masses to the system! The total mass that is being moved must remain constant for every trial.

Analyzing Results 9. Since the force causing the system to accelerate is the weight of the hanger, fill in the column

marked “Force” by calculating the weight of the “Total Hanger Mass” as follows: a. First calculate the column "Total Hanger Mass" by adding the mass of the hanger to the

extra mass you have put on the hanger. Convert your mass to kg, and record in the table.

b. Now that you know the total mass of the hanger in kg, calculate the weight of the hanger and extra masses and record this in the column "Force."

10. Make a graph of Force vs. Acceleration from your data. Make sure you title the graph, include labels & units, and include the linear fit to find the slope of your graphed data. Either print the graph or sketch it (including labels and slopes) below.

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ABRHS PHYSICS (CP) NAME: _________________

Lab 5-2: Newton's Second Law

side 2

Data: Mass of cart, hanger, 2 black bars and all slotted masses: _________ kg NOTE: The Force is equal to the weight of the Total Hanger Mass. Fw = mg & g = 10 m/s2

Extra Mass on Hanger (grams)

Total Hanger Mass (kg)

Force (N)

Acceleration (m/s2)

0 empty hanger =

0.05 kg .50

50 hanger + 50 grams =

0.100 kg

100

150

200

250

300

350

Questions: 1. What is the equation that describes the relationship between acceleration and applied force for

your data? (Remember: slopes have units.) 2. If 1 N = 1 kg•m/s2 show that the units of the slope reduce to kg. 3. What is the physical significance of the slope of your Force vs Acceleration graph? 4. Why did you have to transfer the mass between the cart and the hanger? Why couldn’t you just

add masses to the hanger to increase the applied force? 5. a. If you double the force on an object what will happen to its acceleration? b. If you triple the force on an object what will happen to its acceleration? c. If you halve the force on an object what will happen to its acceleration? d. If you wanted to get 5 times the acceleration on an object, how much force would you need?

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ABRHS PHYSICS (CP) NAME: _________________

Lab 5-3: Newton's Second Law Part 2

side 1

Purpose: To qualitatively determine the relationship between acceleration and mass for an object undergoing a constant applied force.

Materials: 1 (one) 200 gram slotted mass 1 (one) 50 gram slotted mass 2 black bars (500 grams each) 1 string (~75 cm) 1 pulley 1 hanger (50 grams) 1 cart (500 grams) Procedure:

1. Set up the track, cart, pulley, hanger and motion detector as shown in the diagram below.

lab table

empty hanger

empty cart (first trial)> 20 cm

2. Make sure the track is level. The cart should not be rolling in either direction. Also, make sure that the string is attached to the pulley horizontally. (This means the string is over the end bar of the track.)

3. Start LoggerPro. Open up the file “02 Cart.cmbl." Make sure the bottom graph is velocity vs. time.

4. Pull the cart back about 20 cm away from the motion detector. 5. Start collecting data. When you hear the motion detector, release the cart. Don’t let the

cart slam into the end of the track! 6. To determine the acceleration of the cart, measure the slope of the best fit line of the velocity

graph. You will have to highlight the portion of the graph that shows the cart speeding up before you do the linear fit. Record your results in the data table on the other side.

7. Repeat steps 4 to 6 above for five more trials. For each new trial, add 250 grams (0.25 kg) to the cart. Do not add masses to the hanger! (The applied force must remain constant.) If needed, use a little tape to keep the masses from falling off the cart. After determining the acceleration of the cart, record the results in the data table. Don't forget to record the total mass accelerated each time.

8. Make a graph of your results ( Acceleration vs Mass) and either print it or sketch it on the other side of this lab in the conclusions.

Data: Applied force exerted by the 50 gram hanger: 0.50 N

Mass Accelerated (kg)

Acceleration (m/s2)

cart + hanger = .550 kg

cart + hanger + .25 = .800 kg

cart + hanger + 0.5 = 1.05 kg

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ABRHS PHYSICS (CP) NAME: _________________

Lab 5-3: Newton's Second Law Part 2

side 2

Conclusions: 1. What was kept constant in this lab? 2. What did you change each trial? By how much did it change? 3. What did you measure each trial? 4. How did you measure the acceleration of the cart? 5. Where did the force come from that made everything accelerate? 6. There were two other large forces in this lab that we ignored. What were they and why was it ok

to ignore them? 7. Why should you NOT put a linear fit on the graph of acceleration vs mass that you made? 8. So what was the result of your lab? Make it good! Use the words mass, force and acceleration

and include a sketch of your graph.

a

m

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ABRHS PHYSICS (CP) NAME: ______________________

Force Problems I

side 1

1. What net force is needed to accelerate a 100 kg bag 2 m/s2 to the left? 2. What is the acceleration of a 2 kg object if the net force on it is 5 N to the right? 3. What is the acceleration of a 2 kg object if the net force on it is 5 N straight down? 4. A car of mass 1000 kg is accelerating with a constant rate of 1.5 m/s2. What is the net force

acting on the car? 5. An airplane is accelerating down the runway. The mass of the airplane is 15,000 kg. If the

engines are producing a net thrust of 45,000 N, what is the acceleration of the airplane? 6. There is a net force of 200 N acting on a girl on a skateboard. If her acceleration is 4 m/s2, what

is her mass? 7. What net force is needed to accelerate a 5 kg object straight up at 3 m/s2? 8. What is the net force acting on a 1200 kg car that has a constant velocity of 20 m/s? 9. An astronaut in space pushes a 2000 kg satellite with a force of 100 N. What is the acceleration

of the satellite? 10. If a net force of 500 N causes something to accelerate at 15 m/s2, what is its mass? Now some problems where you have to calculate the acceleration first! 11. What net force is needed for a 1700 kg car to go from 0 m/s to 30 m/s in 6 seconds? 12. What net force is needed if a 60 kg person covers 5 meters in 1.3 seconds, assuming she starts

from rest and has a constant acceleration? 13. What net force is needed to accelerate a 4 kg object from 10 m/s to 25 m/s in 5 seconds?

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ABRHS PHYSICS (CP) NAME: ______________________

Force Problems I

side 2

14. What is the net force on a 65 kg person who slides to a stop in a distance of 3.2 meters in 1.5 seconds?

15. You are in your car, mass 1500 kg, traveling down the highway with a speed of 25 m/s. You see

traffic ahead and apply the brakes. You slow down to 15 m/s in 4 seconds. What was the net force on the car?

16. The velocity vs time graph for a 0.75 kg cart is shown

in the diagram to the right:

a. What is the net force on the cart at time 0.1 seconds?

b. What is the net force on the cart at time 0.4 seconds? c. What is the net force on the cart at time 0.7 seconds?

17. The mini-launchers you used in lab fire 0.025 kg steel spheres with a speed of 3 m/s after

pushing them about 0.02 meters. a. What is the net force on a steel sphere while being launched? b. Once it is in the air, what is the net force on the steel sphere?

Answers: 1) 200 N to the left 2) 2.5 m/s2 to the right 3) 2.5 m/s2 down 4) 1500 N 5) 3 m/s2 6) 50 kg 7) 15 N up 8) 0 N 9) 0.05 m/s2 10) 33.3 kg 11) 8500 N 12) 355 N 13) 12 N 14) (–)185 N 15) (–)3750 N (& a = (–)2.5 m/s2) 16. a) 0 N b) 4.5 N c) 0 N 17. a) 5.63 N b) 0.25 N (gravity!)

t (s)

V(m/s)

0.2 0.4 0.6 0.8

2.4

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ABRHS PHYSICS (CP) NAME: ________________ Net Force Concept Sheet

side 1

Key Concepts A. What is meant by the phrase "Net Force?" B. Why is "Net Force" important? C. Can your acceleration be in a different direction than the net force? D. If you are not accelerating, what is the net force on you? Questions 1. You weigh 600 N and are at rest on your skateboard. Show the free-body diagram,

including labels and numbers.

2. You still weigh 600 N, but now a friend is pulling you to the right with a force of 15 N

and also at a constant speed. Show the free-body diagram, including labels and numbers.

15 N

3. There is a normal force of 20,000 N acting on a car at rest. Show the free-body diagram,

including labels and numbers.

4. A person is being pulled to the right at a constant speed. Two of the forces are shown in

the diagram. Complete the free-body diagram, including labels and numbers.

250 N

500 N 6. For each of the following free-body diagrams, what is the net force? Give both the

magnitude and the direction.

100 N75 N

25 N

20 N

20 N

30 N

30 N

8 N

12 N

12 N

13 N

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ABRHS PHYSICS (CP) NAME: ________________ Net Force Concept Sheet

side 2

7. For each of the following free-body diagrams, what is/are the missing force(s) if the net force is as shown?

100 N?30 N

?

60 N

?25 N

?

?

?

15 N

35 N

Fnet = 25 N

Fnet = 25 N Fnet = 10 N Fnet = 25 N

100 N?30 N

?

60 N

?25 N

?

?

?

15 N

35 N

Fnet = 25 N

Fnet = 25 N Fnet = 30 N Fnet = 25 N

8. For each of the following free-body diagrams, what is the acceleration of the mass? Give

both the magnitude and the direction.

200 N130 N

80 N

60 N

60 N

50 N25 N

20 N

3000 N

15,000 N

15,000 N

5000 N

m = 15 kg m = 6 kg m = 2 kg m = 1500 kg

9. For each of the following free-body diagrams, what is/are the missing force(s) if the

acceleration and mass are as shown?

4 N?30 N

?

15 N

??

30 N

100 N

?

200 N

?

m = 1.5 kga = 0.75 m/s2

m = 1.5 kga = 8 m/s2

m = 3 kga = 2 m/s2

m = 20 kga = 4 m/s2

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ABRHS PHYSICS (CP) NAME: ______________________

Force Problems II

Answers: 1) 2 m/s2 2) (–)250 N 3) 10,500 N 4) (–)625 N 5) 1.67 N 6) 4.67 m/s2 7) 1.33 m/s2

1. Tony is pulling Fred, who is sitting in a wagon. Tony is pulling with a force of 250 N. Fred and the wagon have a combined mass of 75 kg. If there is also a frictional force of magnitude 100 N acting on Fred, what is Fred's acceleration?

2. Sasha is pushing Kara with a force 350 N. Kara has a mass of 50 kg. If Kara is accelerating

with a rate of 2 m/s2, what is the force of friction acting on Kara? 3. A car of mass 1500 kg is accelerating with a rate of 3 m/s2. If the magnitude of the force of

friction is 6000 N, how much force must the engine be producing? 4. A 250 kg crate is being pushed with a force of 1000 N. If the crate has an acceleration of 1.5

m/s2, what is the force of friction on the crate? 5. A wooden block of mass 0.35 kg is accelerating at 2.2 m/s2 across a lab table because you are

pulling it. There is 0.9 N of friction acting on the block. With how much force are you pulling the block?

6. Billy is pushing a 150 kg box to the right with a force of 300 N. Bobby is pulling the box to the

right with a force of 400 N. If somehow there was no friction, what is the acceleration of the box? 7. Billy is pushing a 150 kg box to the right with a force of 300 N. Bobby is pulling the box to the

right with a force of 400 N. If this time there was a friction force of 500 N acting on the box, what is the acceleration of the box?

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ABRHS PHYSICS (CP) NAME: ______________________

Pulley Problems 1

Answers: 1) 1.18 m/s2 2) 0.58 kg 3) 2.86 m/s2 4) 1.42 kg 5) 3.00 m/s2 6) 0.16 kg 7) 0.33 kg 8) 1.35 kg

In all of these problems, a cart of mass “m1” is on a horizontal table. There is a second mass “m2” that is connected to the first mass by a string that goes over a pulley. There is no friction.

A. What is Newton’s Second Law? B. In these problems, what is the net force causing the system to accelerate? C. In these problems, what is the mass that is accelerating? D. Turn Newton’s Second Law into an equation that you can use to help solve these problems.

1. If the cart's mass is 1.5 kg and the hanging mass is 0.2 kg, what is the acceleration of the

masses? 2. If the hanging mass is 0.25 kg and the masses are accelerating at 3 m/s2, what is the cart's mass? 3. If the mass on the table is 5 kg and m2 is 2 kg, what is the acceleration of the system? 4. If the hanging mass is 250 grams, and the masses are accelerating at 1.5 m/s2, what is the mass

of the cart? 5. A 150 gram mass is suspended from a string that goes around a pulley and is attached to a mass

of 350 grams, which is resting on a horizontal frictionless table. What is the acceleration of the system?

6. A 0.3 kg mass is is suspended from a string that goes around a pulley and is attached to a second

mass which is on a horizontal frictionless table. If the system is accelerating at 6.5 m/s2, what is the second mass?

*7. If m1 is 1.0 kg and the system is accelerating at 2.5 m/s2, what is the mass m2? *8. If the mass on the table is 2.5 kg and the system is accelerating at 3.5 m/s2, what is the hanging

mass?

m2

m1

table

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ABRHS PHYSICS (CP) NAME: _________________

Friction on a Block

7) 0.5 N 8) 0.169 kg 9) 0.16 N 10) 0.34 N

Imagine that some students are doing an experiment involving forces and friction using the equipment shown below. A wooden block is on a horizontal track and is attached via a pulley to a hanger. In the experiment, they will release the hanger and need to measure the acceleration of the block/hanger in order to be able to calculate the force of friction.

lab table

wooden block

hanger

Concepts 1. We often talk about “the system” in physics problems. A system is two or more objects that have

the same motion (speeds and accelerations) because they are connected in some way. In this situation, what is the system?

2. If this was a lab, and I asked you to measure the acceleration of the system, how could you do it? 3. There are four big forces that are affecting the system. What are they? Be specific. 4. Two of those big forces cancel each other out. What are they? 5. What force is trying to speed up the system and cause the motion? 6. What force is trying to slow down the system and fight the motion? Calculations For the calculations below, use the following numbers:

Mblock = 119 grams mhanger = 50 grams asystem = 0.934 m/s2. 7. What is the applied force on the system? (i.e. Calculate the force that is trying to accelerate the

system?) 8. What is the mass of the system? 9. What is the net force on the system? 10. What is the force of friction on the system?

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ABRHS PHYSICS (CP) NAME: ___________________

Lab 5-4: Finding Friction @School

side 1

Purpose: Devise a method to calculate the force of friction between a wooden block and the lab tracks when the block is pulled across the track by a hanger.

lab table

wooden block

hanger

Procedure: Attach a string to a wooden block and attach a pulley to the end of the table. Put a hanger (and enough extra mass) on the end of the string so that it accelerates the wooden block across the table. Devise a method to calculate the force of friction that is acting on the block. In the space below, describe what you will try to measure, how you will measure it and what equipment you will need. When your group is done, show your teacher. Be prepared to also explain how you will analyze your data to ultimately calculate the force of friction on the block. Other Equipment Needed: Procedure: Data: Teacher OK: ________ Analysis & Conclusion:

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ABRHS PHYSICS (CP) NAME: ___________________

Lab 5-5: Finding Friction @Home

side 1

Purpose: Devise a method to calculate the force of friction between you wearing socks and a smooth, wooden floor in your house. Procedure: Devise a method to calculate the force of friction that is acting on you when you are just wearing socks on a smooth wooden floor. In the space below, describe what you will try to measure, how you will measure it and what equipment you will need. When your group is done, show your teacher. Be prepared to also explain how you will analyze your data to ultimately calculate the force of friction. Equipment Needed: Procedure: Data: Teacher OK: ________ Analysis & Conclusion:

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ABRHS PHYSICS (CP) NAME: ______________________

Pulley Problems 2

side 1

In all of these problems, a mass “m1” is on a horizontal table. There is a second mass “m2” that is connected to the first mass by a string that goes over a pulley. There is friction between the mass on the table and the table, (which we can call “f”)

A. What is Newton’s Second Law? B. In these problems, what is the force causing the system to accelerate? C. In these problems, what is the force trying to stop the acceleration? D. So in these problems, what is the net force on the system? E. In these problems, what is the mass that is accelerating? F. Turn Newton’s Second Law into an equation that you can use to help solve these problems.

1. If the mass on the table is 1.25 kg, the hanging mass is 0.3 kg and there is a frictional force of 2

N, what is the acceleration of the system? 2. If the mass on the table is 0.75 kg, the hanging mass is 0.15 kg and the system is accelerating at

0.8 m/s2, what is the force of friction? 3. If the hanging mass is 0.4 kg, the force of friction is 2.5 N and the system is accelerating at 0.7

m/s2, what is mass on the table? 4. If both masses are 5 kg, and the system is accelerating at 3 m/s2, what is the force of friction? 5. If m1 is 0.3 kg and m2 is 0.5 kg and there is a frictional force of 1.5 N, what is the acceleration of

the system?

m2

m1

table

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ABRHS PHYSICS (CP) NAME: ______________________

Pulley Problems 2

side 2

6. If m1 is 2.2 kg and m2 is 750 grams and the system is accelerating at 1.6 m/s2, what is the force of friction?

7. If the hanging mass is 500 grams, there is a frictional force of 2.2 N and the system is

accelerating at 1.7 m/s2, what is the mass on the table? 8. A mass of 250 grams is suspended from a string that goes around a pulley and is connected to a

mass of 900 grams. The 900 gram mass is on a horizontal table and there is a frictional force of 1.8 N. What is the acceleration of the system?

9. A 1.1 kg mass is hanging from a string connected via a pulley to a mass of 0.75 kg which is on a

horizontal table. If the system is accelerating at 4.5 m/s2, what is the force of friction? *10. If m1 is 1.2 kg and there is a frictional force of 6 N and the system is accelerating at 0.9 m/s2-,

what is the mass m2? Answers: 1) 0.65 m/s2 2) 0.78 N 3) 1.74 kg 4) 20 N 5) 4.38 m/s2 6) 2.78 N 7) 1.15 kg 8) 0.61 m/s2 9) 2.68 N 10) 0.78 kg

Page 21: ABRHS P AME Chapter 5: Newton’s Second La · Chapter 5: Newton’s Second Law 2015-16 ... A dragster starts from rest and has a constant acceleration of 7 m ... A bicyclist traveling

ABRHS PHYSICS (CP) NAME: ______________________

Force Problems III

side 1

Numbers 1 to 7 refer to the diagram below, which shows a hand holding up a 4 kg mass by a string.

1. Imagine you pull up on the mass with a force of 40 N. (We would call this force the tension in the string). a. What is the weight of the mass? b. So what is the net force on the mass? c. So what is the acceleration of the mass?

2. If you pull up on the mass with a force of 60 N, what is the acceleration of the mass? 3. If you pull up on the mass with a force of 30 N, what is the acceleration of the mass? 4. If the mass is accelerating up, what has to be true about the tension in the string? 5. If the mass is accelerating down, what has to be true about the tension in the string? 6. If the mass has a constant speed, what has to be true about the tension in the string? 7. If the mass is accelerating up at 1.5 m/s2, what is the tension in the string? Enough with strings, but now some problems with friction. Numbers 8 to 11 refer to the following diagram:

2.5 kg Fa = 10 N

8. What is the force of friction if the acceleration of the block is 4 m/s2? 9. What is the force of friction if the acceleration of the block is 0 m/s2? 10. What is the force of friction if the acceleration of the block is 3 m/s2?

4 kg

Page 22: ABRHS P AME Chapter 5: Newton’s Second La · Chapter 5: Newton’s Second Law 2015-16 ... A dragster starts from rest and has a constant acceleration of 7 m ... A bicyclist traveling

ABRHS PHYSICS (CP) NAME: ______________________

Force Problems III

side 2

Numbers 11 to 15 refer to the following diagram:

2.5 kg

frictionless

Fa = 20 N

11. What is the acceleration of the block if the angle is 0º? 12. What is the acceleration of the block if the angle is 20º? 13. What is the acceleration of the block if the angle is 40º? 14. What is the acceleration of the block if the angle is 60º? 15. What is the acceleration of the block if the angle is 90º? Careful! Numbers 16 to 18 refer to the following diagram:

Fam

16. A 5 kg block is pulled with a force of 75 N at an angle of 30º. There is also 20 N of friction acting

on the block. What is the acceleration of the block? 17. A 12 kg block is pulled with a force of 100 N at an angle of 45º. There is also 40 N of friction

acting on the block. What is the acceleration of the block? 18. A 25 kg block is pulled with a force of 120 N at an angle of 30º. How much friction is there if the

acceleration of the block is 3 m/s2? Answers: 1.a) 40 N b) 0 N c) 0 m/s2 2) 5 m/s2 up 3) 2.5 m/s2 down 4) Tension > weight 5) Tension < weight 6) Tension = weight 7) 46 N 8) 0 N 9) 10 N 10) 2.5 N 11) 8 m/s2 12) 7.52 m/s2 13) 6.13 m/s2 14) 4.00 m/s2 15) 0 m/s2 16) 8.99 m/s2 17) 2.56 m/s2 18) 28.9 N