You hold an object weighing 10 N so that it is at rest.
How much work do you do on the object? How much work does gravity do on the object?

The work you do is:

1. zero
2. positive
3. negative

Both you and gravity do zero work, because the displacement is zero.

You raise the 10 N object 0.5 m vertically. The object starts and ends at rest.

How much work do you do on the object?

1. 5 J (31/34) (91%)
2. More than 5 J (3/34) (9%)
3. Less than 5 J (0/34) (0%)

Both the initial and final kinetic energy is zero. The change in potential energy is 5 J, and that comes from the work you do. You do 5 J worth of work.

You move the 10 N object 2 m horizontally. The object starts and ends with the same speed.

How much work does gravity do on the object? How much work do you do on the object?

The work you do on the object is:

1. 0 (18/33) (55%)
2. 20 J (12/33) (36%)
3. some positive value (3/33) (9%)
4. some negative value (0/33) (0%)

Your upward force and the downward force of gravity are perpendicular to the displacement, so neither force does any work.

A car traveling at an initial speed v on a flat road comes to a stop in a distance L once the brakes are applied. Friction is the force that brings the car to rest. Assuming the same force is applied, how far does the car travel once the brakes are applied if the initial speed is 2v?

1. L x 2^½ (2/23) (9%)
2. 2L (6/23) (26%)
3. 3L (1/23) (4%)
4. 4L (14/23) (61%)

The answer is 4L. The kinetic energy has increased by a factor of 4, so the work required to bring the car to rest must increase by a factor of 4. If the force is unchanged the distance must increase by a factor of 4.