- #1
cowmoo32
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Homework Statement
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?
Homework Equations
(1) d = V0t + 0.5at2
(2) F=ma
(3) W = Fd
(4) P = W/Δt
The Attempt at a Solution
(1) a = 17m/sec2
(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.