(Multiple choice)

(1) True or false:

(a) The total energy of a system cannot change. 

(b) When you jump into the air, the floor does work on you, increasing your potential energy.

(2)

A body falling through the atmosphere (air resistance is present) gains 20 J of kinetic energy. The amount of gravitational potential energy that is lost is 

(a) 20 J. 

(b) More than 20J. 

(c) Less than 20 J. 

(d) Impossible to tell without knowing the mass of the body. 

(e) Impossible to tell without knowing how far the body falls.

(3)

A block of mass m, starting from rest, is pulled by a string up a frictionless inclined plane that makes an angle θ with the horizontal. The tension in the string is T and the string is parallel to the plane. After traveling a distance L, the speed of the block is v. The work done by the tension T is

(a) mgL θ

(b) mgL cos θ + ½mv² 

(c) mgL sin θ + ½mv²

(d) mgL cos θ

(e) TL cos θ

(4)

A block of mass m slides with constant velocity v down a plane inclined at θ with the horizontal. During the time interval ∆t, what is the magnitude of the energy dissipated by friction?

(a) mgv Δt tan θ

(b) mgv Δt sin θ

(c) ½mv² Δt 

(d) The answer cannot be determined without knowing the coefficient of kinetic friction.

(5)

Assume that on applying the brakes a constant frictional force acts on the wheels of a car. If that is so, it follows that 

(a) The distance the car travels before coming to rest is proportional to the speed of the car before the brakes are applied.

(b) The car's kinetic energy diminishes at a constant rate. 

(c) The kinetic energy of the car is inversely proportional to the time that has elapsed since the application of the brakes. 

(d) None of the above applies.