E. Circular Motion Take Home Quiz

300 points (15 points/question)

 

1. A flywheel, of radius 1 m, is spinning with a constant angular velocity of 2 rad/s. What is the centripetal acceleration of a point on the wheel's rim?

a. 1m/s2

b. 2 m/s2

c. 4 m/s2

d. None of the above

 

2. A fan blade, whose diameter is 1 m, is turning with an angular velocity of 2 rad/s. What is the tangential velocity of a point on the tip of the blade?

a. 2 m/s

b. 0.5 m/s

c. 1 m/s

d. None of the above

 

3. What is the angular speed of a record that rotates at 33-1/3 rpm? (Hint: Convert 33 1/3 RPM into radians. Remember that RPM means rotations/minute)

a. 33.3/ rad/s

b. 1.74 rad/s

c. 2.77 rad/s

d. 3.49 rad/s

 

4. The banking angle in a turn on the Olympic bobsled track is not constant, but increases upward from the horizontal. Coming around a turn, the bobsled team will intentionally "climb the wall," then go lower coming out of the turn. Why do they do this?

a. To give the team better control, because they are able to see ahead of the turn.

b. To prevent the bobsled from turning over.

c. To take the turn at a faster speed.

d. To reduce the g-force on them.

 

5. A horizontal curve on a bobsled run is banked at a 45 angle. When a bobsled rounds this curve at the curve's safe speed (no friction needed to stay on the run), what is its centripetal acceleration?

a. 1.0 g

b. 2.0 g

c. 0.5 g

d. None of the above

 

6. Does the centripetal force acting on an object do work on the object?

a. Yes, since a force acts and the object moves, and work is force times distance.

b. Yes, since it takes energy to turn an object.

c. No, because the object has constant speed.

d. No, because the force and the displacement of the object are perpendicular.

 

 

7. A roller coaster car is on a track that forms a circular loop in the vertical plane. If the car is to just maintain contact with track at the top of the loop, what is the minimum value for its centripetal acceleration at this point?

a. g downward

b. 0.5 g downward

c. g upward

d. 2 g upward

 

8. A roller coaster car (mass = M) is on a track that forms a circular loop (radius = r) in the vertical plane. If the car is to just maintain contact with the track at the top of the loop, what is the minimum value for its speed at that point?

a. 2 Mrg

b.

c.

d. None of the above

 

9. The speed needed at the bottom of a loop-the-loop track so that a car can coast to the top, with sufficient speed to stay on the track, depends on the mass of the car. (Neglect the effects of friction.)

a. Always true.

b. Never true.

c. Sometimes true, since kinetic energy is a function of mass.

d. Sometimes true, since potential energy is a function of mass.

 

10. The net force on an object in orbit is zero.

a. True

b. False

 


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11. A planet revolves clockwise around a star, with constant speed. The direction of its acceleration at point P is

a. graph A

b. graph B

c. graph C

d. graph D

 


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12. A girl attaches a rock to a string, which she then swings counter-clockwise in a horizontal circle. The string breaks at point P on the sketch, which shows a bird's-eye view (i.e., as seen from above). What path will the rock follow?

a. A

b. B

c. C

d. D

e. E

 

 

13. Marilyn (M) and her sister Sheila (S) are riding on a merry-go-round, as shown (bird's-eye view).

a. They have the same speed, but their angular velocity is different.

b. They have different speeds, and different angular velocities.

c. They have different speeds, but the same angular velocity.

d. They have the same speed and the same angular velocity.

 


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14. The record playing on the turntable of your stereo is rotating clockwise (as seen from above). After turning it off, your turntable is slowing down, but hasn't stopped yet. The direction of the acceleration of point P (at the left) is: (Hint: It is slowing down! What does that do to its net direction of acceleration)

a. graph A

b. graph B

c. graph C

d. graph D

 

15. What condition or conditions are necessary for rotational equilibrium?

a. SFx = 0

b. SFX = 0, SFY = 0, St = 0

c. St = 0

d. SFY = 0

e. SFx = 0, SFY = 0

 


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16. What condition or conditions are necessary for static equilibrium?

a. SFx = 0

b. SFX = 0, SFY = 0, St = 0

c. St = 0

d. SFY = 0

e. SFx = 0, SFY = 0

 

17. A heavy boy and a lightweight girl are balanced on a massless seesaw. If they both move forward so that they are one-half their original distance from the pivot point, what will happen to the seesaw?

a. The side the boy is sitting on will tilt downward.

b. The side the girl is sitting on will tilt downward.

c. Nothing, the seesaw will still be balanced.

d. It is impossible to say without knowing the masses and the distances.

 

18. The condition for rolling without slipping is that:

a. VCM = 2 rw

b. VCM = rw2

c. VCM = rw/2

d. VCM = rw

 

19. Consider a rigid body that is rotating. Which of the following is an accurate statement?

a. Its center of rotation is its center of gravity.

b. All points on the body are moving with the same angular velocity.

c. All points on the body are moving with the same linear velocity.

d. Its center of rotation is at rest, i.e., not moving.

 

20. Consider a car with its wheels rolling (not sliding) on the road. How fast must the auto move for some point on a wheel to reach the speed of sound? (hint: Look at fig 8.1 on p. 252)

Answer: The car must travel at _______ times the speed of

sound. Explain.