Two students each carry a box up to the third ?oor of a building. The total mass of each student and the box she is carrying is the same. Roberta makes the trip in 45 s while Mary takes 30 s. Which of the following statements best describes this task?
A)Roberta does more total work than Mary.
B)Mary does more total work than Roberta.
C)Roberta has a greater power output than Mary.
D)Mary has a greater power output than Roberta.

Question

Quizplus · Accepted Answer

The total work done by both Roberta and Mary is the same since work is defined as force times distance, and both the force (equal to the weight of the student plus the box) and the distance (height of the building) are the same for both. However, power is defined as work done per unit time. Since Mary takes less time (30 s) to do the same amount of work as Roberta (45 s), Mary has a greater power output.

Two Students Each Carry a Box Up to the Third