Power Question

Question

5. The observation platform at the top of the Eiffel tower is 290 m above the ground.
a) How much work must the average person perform to climb to this level? Assume that an average person has a mass of 70 kg.



b) Would the amount of work done above be different if you stopped for a rest from time to time? Explain your answer.



c) Would the amount of work change if you ran up some stairs and walked up others? Explain your answer.



d) Repeat (b) and (c) above by replacing the work “work” with power.

 

Question (b)


Questions (c)

Answer 1

Work = F (cosΘ) x D F is force, D is the distance over which the force is applied, Θ is the angle between the direction of the Force and the direction of the motion.

Assume here that the person is climbing straight up the building at an angle perpendicular to the ground since we weren't given the angle of motion.

 

The Force in this case will be the Force of gravity pulling down on the person.

F = mass x acceleration of gravity

F = 70 kg x 9.8 m/s2 = 686 Newtons (N)

The direction of motion is straight up which is an angle of 180◦ from the direction of the force which is straight down.
So:
W = 686 (cos 180◦ ) x D The distance is 290 m
So:
W = 686 (cos 180◦ ) x 290
W = -198940 J

This answer should be reported with only 3 significant figures so the answer is:

W = -1.99 X 105 J

B. No. The amount of work depends only on the distance travelled and the force applied. Work is independent of the amount of time it takes to get to the top.

C. . No. The amount of work depends only on the distance travelled and the force applied. Work is independent of the amount of time it takes to get to the top.

D. Repeat B replacing work with power

Power = Work/time

This means that the Power output will change if the time the person takes to get to the top changes
E. Same answer as D.