P.Exam 2

Two men, Joel and Jerry, push against a wall. Jerry stops after 10 min, while Joel is able to push for 5.0 min longer. Compare the work they do. A) Neither of them does any work. B) Both men do positive work, but Joel does 25% more work than Jerry. C) Both men do positive work, but Jerry does 50% more work than Joel. D) Both men do positive work, but Joel does 75% more work than Jerry. E) Both men do positive work, but Joel does 50% more work than Jerry.

A

A ball drops some distance and gains 30 J of kinetic energy. Do NOT ignore air resistance. How much *gravitational potential energy* did the ball lose? A) less than 30 J B) more than 30 J C) exactly 30 J

B

A ball drops some distance and loses 30 J of gravitational potential energy. Do NOT ignore air resistance. How much *kinetic energy* did the ball gain? A) exactly 30 J B) less than 30 J C) more than 30 J

B

A string is attached to the rear-view mirror of a car. A ball is hanging at the other end of the string. The car is driving around in a circle, at a constant speed. Which of the following lists gives all of the forces directly acting on the ball? A) tension, gravity, the centripetal force, and friction B) tension and gravity C) tension, gravity, and the centripetal force D) tension

B

You are standing in a moving bus, facing forward, and you suddenly fall forward as the bus comes to an immediate stop. As seen from a stationary observer at the bus stop, the force acting on you that causes you to fall forward is A) the force due to kinetic friction between you and the floor of the bus. B) No forces were acting on you to cause you to fall. C) the force due to static friction between you and the floor of the bus. D) the normal force due to your contact with the floor of the bus. E) the force of gravity.

B

A stalled car is being pushed up a hill at constant velocity by three people. The net force on the car is A) up the hill and equal to the weight of the car. B) up the hill and greater than the weight of the car. C) zero. D) down the hill and equal to the weight of the car. E) down the hill and greater than the weight of the car.

C

Is it possible for a system to have negative potential energy? A) No, because the kinetic energy of a system must equal its potential energy. B) No, because this would have no physical meaning. C) Yes, since the choice of the zero of potential energy is arbitrary. D) Yes, as long as the total energy is positive. E) Yes, as long as the kinetic energy is positive.

C

Two objects have masses m and 5m, respectively. They both are placed side by side on a frictionless inclined plane and allowed to slide down from rest. A) It takes the lighter object 10 times longer to reach the bottom of the incline than the heavier object. B) It takes the heavier object 10 times longer to reach the bottom of the incline than the lighter object. C) It takes the heavier object 5 times longer to reach the bottom of the incline than the lighter object. D) The two objects reach the bottom of the incline at the same time. E) It takes the lighter object 5 times longer to reach the bottom of the incline than the heavier object.

D

If two nonzero vectors point in the same direction, their dot product must be zero. True or false?

false