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# Mechanics and Gravitation: 17 Multiple Choice Questions

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(See attached file for full problem description)

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Mark the following statements true or false.

1. (b) A conservative force can do no work on an object.

2. (a) Potential energy is necessarily a positive quantity.

(b) Kinetic energy is necessarily a positive quantity.

(c) The change in potential energy of an object is equal to the net work done on the object.

3. (a) I pick up a 50-lb crate and set it on a shelf 4ft off the floor. The mechanical energy of the crate is conserved.
4. (a) The centripetal acceleration of an object undergoing circular motion is always directed toward the center of the circle.

The rest are multiple choice.

5. A ball (I=2/5 mr^2) and a hoop (I=mr^2), both with the same mass, are rolled up an incline with the same initial kinetic energy . Therefore,
a. The ball goes further
b. The hoop goes further
c. The ball and hoop go the same distance
d. There is no way to tell which object goes farther, because the radii of the objects aren't given.

6. The necessary condition for the conservation of angular momentum of an object is
a. no net work is done on the object by conservative forces.
b. No net work is done on the object by any non-conservative forces.
c. No net work is done on the object by any force.
d. The net external torque on the object is zero.
e. The net external torque and force acting on the body is zero

7. The net work expended to accelerate a car from 0to 30m/s
a. is equal to that required to accelerate it from 30m/s to 60 m/s
b. is more than that required to accelerate it from 30m/s to 60m/s
c. is less than that required to accelerate it from 30m/s to 60m/s
d. can be a,b, or c, depending on the time taken for the acceleration

8. A planet has two moon with identical mass. Moon 1 is in a circular orbit of radius r. Moon 2 is in a circular orbit of radius 2r. The magnitude of the gravitational force exerted by the planet on Moon 2 compared to the gravitational force exerted by the planet on Moon 1 is
a. four times as large
b. twice as large
c. half as large
d. one-fourth as large

9. We read that the period of earth satellite A is 3 hours and the period of earth satellite B is 6 hours. Therefore, from Kepler's 3rd law, we can conclude that
a. The speed of A is twice the speed of B
b. A is closer to earth than is B
c. B is closer to earth than is A
d. The speed of B is greater than the speed of A
e. A and B sweep out equal areas around the earth in equal time.

10. A ball with a mass of .150kg if traveling initially at 14.0 m/s to the right collides head-on with a .300kg ball that is initially at rest. After the collision, the first ball is found to have a speed of 2.30m/s to the left. What is the speed of the second ball after the collision.
a. 8.15m/s
b. 9.68m/s
c. 4.03m/s
d. 11.8m/s
e. 5.8m/s

11. A hoop (I=mr^2) of mass 25kg rolls without slipping. If the center of mass of the hoop has a translational speed of 4.0m/s the total kinetic energy of the hoop is
a. 0.20kJ
b. 0.40kJ
c. 0.60kJ
d. 1.1kJ
e. 3.0kJ

12. A space station is constructed in the shape of a wheel with a diameter of 200. m. What angular velocity must the station have to produce an "artificial gravity" at the rim of 9.80m/s^2.

13. A wheel slows from 20 rad/s to 12 rad/s in 5 seconds under the influence of a constant frictional torque. In these 5 seconds, through what angle (in radians) does the wheel turn?

14. Suppose you exert a force of 180N tangentially to a 0.280 m radius 75 kg grindstone (I =mr^2/2). What is the angular acceleration assuming negligible opposing friction.

15. The head of a 200-g golf club is traveling at 55 m/s just before it strikes a 46-g golf ball at rest on a tee. After the collision, the club head travels ( in the same direction) at 40 m/s.
What is the speed of the golf ball right after impact
a. 65 m/s
b. 78 m/s
c. 89 m/s
d. 102 m/s

16. The distance (from the center of the earth) that a satellite orbits the earth is doubled by NASA so that it can perform a new mission. The new gravitational force exerted by the earth on the satellite is ____ times the original gravitational force.
a. 2.0
b. 1.414
c. 0.25
d. 4.0
e. 0.50

17. A 40-kg girl, standing at rest in ice, gives a 60-kg boy, who is standing at rest on the ice, a shove. After the shove, the boy is moving backwards at 2.0 m/s. Ignoring friction, what is the girl's speed after the shove.
a. zero
b. 1.3 m/s
c. 2.0 m/s
d. 3.0 m/s
e. 6.0 m/s
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