2011 Chapter 8 Chart Homework

Quantity Old SymbolWith unit

Old Formula(s) Angular (new)SymbolWith unit

Angular (new) formula(s)

Equation that relates the old symbol with the new symbol

Mass kgm2

I=mr2

What is r in this formula?

What is m?

What is I?

Force F=ma

F= net force (N)

m= mass (kg)

a=acceleration (m/s2)

m

=

What is τ?

What is I?

What is α?

What is τ?

What is F?

What is d?

Kinetic Energy

KJoules

KJoules

Momentum Lkgm2/s

L=ImvrWhat is I?What is ω?What is m?What is v?What is r?

L= p dL= angular momentum (kgm2/s)p=momentum (kgm/s)d=lever arm (m)

Name______________________

2011 Chapter 8 Chart Homework

Fill in the following chart using what you already know and Chapter 8 for new information (skip any crossed out boxes).

2011 Chapter 8 Chart Homework1. Where is the center of gravity of an object?

2. Why can’t you put your heels firmly against a wall and then bend over without falling?

3. When you carry a heavy load- such as a pail of water-with one arm, why do you tend to hold your free arm out horizontally?

4. What is moment of inertia?

5. If you walked along the top of a fence, why would holding your arms out help you to balance?

6. What is an axis of rotation?

7. Arlo walks up to a door and is unsure where the hinge is. If he pushes the side of the door that is the hinge what happens? What if he pushes the side of the door that is opposite the hinge? What if he pushes the center of the door?

8. What is a torque?

a. Formula?

b. What is the lever arm?

c. Why sin θ?

d. Units for torque

e. Vector or scalar? When is torque positive? Negative?

2011 Chapter 8 Chart Homework

9. Shown below are seven situations where a student is holding a meter stick straight out horizontally. All of the meter sticks are identical, but the number, mass and locations (either at the 50 cm mark or at the other end of the meters stick from the student) of the objects hung on the sticks vary. Rank these situations form greatest to least, on the basis of how difficult it would be for the student to keep the meter stick from rotation.

10. Explain how an orthodontist uses torque to straighten or realign teeth.

11. Which is better for prying open a stuck cover from a can of paint- a screwdriver with a thick handle or one with a long handle?

12. Which is better for turning stubborn screws- a screwdriver with a thick handle or one with a long handle?

13. Most doorknobs are placed on the side of the door opposite the hinges instead of in the center of the door. If a torque of 1.2 Nm is required ot open a door, how much force must be exerted on a doorknob 0.76 m from the hinges compared to the doorknob in the middle of the door 0.38 m from the hinges?

2011 Chapter 8 Chart Homework14. Shown below are seven situations where a student is holding a meter stick at the left end at various

angles. A 1000g mass is hung on the meter sticks at different locations. All of the meter sticks are identical, but the distance along the meter stick at which the 1000 g mass is hung and the angles at which the student holds the meter stick vary. Rank these situations, from greatest to least, on the basis of how difficult it would be for the student to hold the meter stick form the left end in the position shown.

15. A simple pendulum consists of a 3 kg point mass hanging at the end of a 2 meter long light string that is connected to a pivot point. Calculate the magnitude of the torque (due to the force of gravity) around this pivot point when the string makes a 5 degree angle with the vertical.

16. Alice and Arlo are children playing on a seesaw. Alice is 300N, and Arlo is 600N. If Alice is 3 meters for the fulcrum, where should Arlo sit for them to balance?

2011 Chapter 8 Chart HomeworkEnergy

17. What is the new formula for kinetic energy?

18. The net work done in accelerating a propeller from rest to an angular speed of 200 rad/s is 3000J. What is the moment of inertia of the propeller?

19. What is angular momentum?

a. Formula?

b. What is the lever arm?

c. Units for angular momentum?

d. Vector or scalar? When is angular momentum positive? Negative?

20. Often when a high diver wants to turn a flip in midair, she draws her legs up against her chest. Why does this make her rotate faster? What should she do when she wants to come out of her flip?

21. Alice, the ice skater, spins around in the rink at 1.2 m/s with each of her arms stretched out 0.70m from the center of her body. In each hand she holds a 1.0 kg mass. If angular momentum is conserved, how fast will Alice begin to spin if she pulls her arms to a position 0.15 m from the center of her body?

2011 Chapter 8 Chart Homework

Pressure/Force/Area (Chapter 9)1. What is pressure?

a. Formula?

b. Vector or scalar?

c. Units?

2. A 70 kg man sits in a 5 kg chair so that his weight is evenly distributed on the legs of the chair. Assume that each leg makes contact with the floor over a circular area with radius of 1.0cm. What is the pressure exerted on the floor by the chair?

3. Explain Pressure/force/area demonstrationa. Egg with flask

b. Hemispheres

c. Balloon in vacuum

d. Marshmallows in vacuum

e. Apple with straw

f. Bed of nails