Work Energy and Power

Consider the statements below:

I Work is done on an object when a force displaces the

object in the direction of the force.

II Mechanical energy of a system is conserved when an

external force does no work on the system.

III The work done on an object by a net force is equal to

the kinetic energy of the object.

Which of the above statements is/are TRUE?

• Only I

• I and II only

• II and III only

• I, II and III

A trolley moves from rest on a frictionless track, as indicated. Which graph represents the mechanical energy (E) versus the distance (D) as it moves along the track the best?

• 
• 
• 
• 

The engine of a car does work, W, to increase the velocity of the car from 0 to v. The work done by the engine to increase the velocity from v to 2v, is:

• W

• 2W

• 3W

• 4W

The kinetic energy of a car moving at constant velocity v is K. The velocity of the car changes to 2v. What is the new kinetic energy of the car?

• $\frac{1}{4}K$

• $\frac{1}{2}K$

• 2K

• 4K

The graph below represents a constant force F acting on an object over a displacement x. The force and displacement are in the same direction. Which ONE of the following statements can be deduced from the graph?

• The gradient of the graph represents the work done by the force.

• The gradient of the graph represents the change in kinetic energy of the object.

• The area under the graph represents the net work done by the force.

• he area under the graph represents the power dissipated by the force.

An object moves in a straight line on a ROUGH horizontal surface. If the net work done on the object is zero, then …

• the object has zero kinetic energy.

• the object moves at constant speed.

• the object moves at constant acceleration.

• there is no frictional force acting on the object.

A car moves up a hill at CONSTANT speed. Which ONE of the following represents the work done by the weight of the car as it moves up the hill?

• ΔEk

• ΔEp

• −ΔEk

• −ΔEp

A car moves up a hill at CONSTANT speed. Which ONE of the following represents the work done by the weight of the car as it moves up the hill?

• ΔEk

• ΔEp

• −ΔEk

• −ΔEp

Power is defined as the rate …

• of change of velocity.

• at which work is done.

• of change of momentum.

• of change of displacement.

Power is defined as the rate …

• of change of velocity.

• at which work is done.

• of change of momentum.

• of change of displacement.