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

A 7-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. If the box is lifted, at constant acceleration, from rest on the floor to a height of 1.5 m above the floor in 0.42 s, what average power is delivered by the person pulling on the rope?

2. Relevant equations

(1) d = V_{0}t + 0.5at^{2}

(2) F=ma

(3) W = Fd

(4) P = W/Δt

3. The attempt at a solution

(1) a = 17m/sec^{2}

(2)

F = 7*17

F = 119

(3)

W = 119*1.5

W = 178.5

(4)

P = 178.5/0.42

P = 425

Here's the thing, that answer agrees with the equation in the solution manual, but not on my homework. I'm reworking an old problem and I got it correct the first time around and can't figure out how I arrived at the answer, which is 0.67kW.

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# Lifting a Box - Work and Power

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