Question

Use the following prompt for questions #9-10:
A second piano with the same mass is lifted 10m above the ground in 15 s by a forklift. Givens:
9. Which does the most work, the crane from the previous question, or the forklift? Explain.
10. Which expends the most power, the crane or the forklift? Explain

Answer 1

9. They do the same amount of work. Work to lift mass m through height h is W = mgh, which depends only on mass and height (and g). Both pianos have the same m and are lifted the same h, so W is the same.

10. Power = work/time, P = W/t = mgh/t. Since W is the same, the machine that takes less time delivers more power. So whichever (crane or forklift) lifts the piano in the shorter time expends the greater power. (Numerically, the forklift’s power is P_f = mgh/15 s; the crane’s is P_c = mgh/t_crane, so compare t_crane to 15 s.)