SAT Subject Physics Practice Question 472: Answer and Explanation
3. An Olympic weight lifter lifts a weight bar weighing 2000N straight up to a height of 2.25 m in a time of .65 seconds. The weight lifter stands holding the weight at that height for the next 4 seconds before dropping the weights to the floor.
How much power did the weight lifter use to lift the weights overhead?
A. 2925 watts
B. 3077 watts
C. 4500 watts
D. 6923 watts
E. 9100 watts
Correct Answer: D
The correct answer is (D). Power is the rate at which work is done, Power = work/time. The weight lifter lifted the weights up from the floor to a distance of 2.25 m above the floor in a time of .65 seconds. The work the weight lifter did to raise the weights can be calculated either by (F·s·cosθ) or by using the potential energy (mgh). Divide the work by the time he took to raise the weights, and the power he develops is 6923 watts.