(adsbygoogle = window.adsbygoogle || []).push({}); 1. The problem statement, all variables and given/known data

A 7.5 kg box is being lifted by means of a light rope that is threaded through a single, light, frictionless pulley that is attached to the ceiling.

a) If the box is being lifted at a constant speed of 2.0 m/s, what is the power delivered by the person pulling on the rope?

b) If the box is lifted, at constant acceleration, from rest on the floor to a height of 1.5m above the floor in 0.42 s, what average power is delivered by the person pulling on the rope?

2. Relevant equations

k = 1/2 m v^2 (velocity vector)

d = initial velocity(t) + 1/2at^2

v = initial velocity + at

3. The attempt at a solution

My answer for a is 15 Joules. I basically just plugged in the numbers for this one, since we are only going in the y direction I didn't bother writing ( 0i + 2.0j)

k = (1/2)(7.5)(2.0)^2 = 15 Joules

My answer for b is 190 Joules. For this one I found the acceleration and then the velocity and plugged in those numbers.

1.5 = 1/2a(0.42)^2

a = 17 m/s^2

v = 17(0.42) = 7.1 m/s

k = 1/2 (17) (7.1)^2 = 190 Joules

Can anyone tell me if these answers are correct?

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# Work and power

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