9. Work & Energy

Which one of the following phrases best describes the term $\mathrm{work} \mathrm{function}$?

A motor lifts a $1500\mathrm{kg}$ elevator vertically upward a height of $100m$. Assuming the acceleration due to gravity is $9.8m/s^2$ and neglecting friction, how much work does the motor do?

In which of the following scenarios is the greatest amount of work done on a wagon as it is pulled up an inclined plane of height $h$ and length $L$ at constant speed, neglecting friction?

In which of the following situations is no work done by the applied force on the object?

In pedaling a bicycle uphill, a cyclist exerts a downward force of 420 N during each stroke. If the diameter of the circle traced by each pedal is 36 cm, calculate how much work is done in each stroke.

A satellite moves in a stable circular orbit around $Earth$ under the influence of gravity. How much work is done by the gravitational force on the satellite during one complete revolution?

In which of the following cases is no work done on the football?

A gust of wind blowing east pushes against a ball. When will the wind do $W$ (work) on the ball?

Assume a cyclist of weight mg can exert a force on the pedals equal to 0.90 mg on the average. If the pedals rotate in a circle of radius 18 cm, the wheels have a radius of 34 cm, and the front and back sprockets on which the chain runs have 42 and 19 teeth respectively (Fig. 7–33), determine the maximum slope of a hill the cyclist can climb at constant speed. Assume the mass of the bike is 12 kg and that of the rider is 65 kg. Ignore friction. Assume the cyclist’s average force is always: downward.

If the hill in Example 7–2 (Fig. 7–4) was not an even slope but rather an irregular curve as in Fig. 7–23, show that the same result would be obtained as in Example 7–2: namely, that the work done by gravity depends only on the height of the hill and not on its shape or the path taken.