You are loading freight on the back of large truck by lifting boxes using a ligh

Question

You are loading freight on the back of large truck by lifting boxes using a light rope that is threaded through a single, light, frictionless pulley that is attached to the ceiling. Each box has a mass of 6 kg and is 0.8 m tall.

(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?

I think the answer here is .117 kw

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?

______KW PLEASE I KEEP GETTHING THIS ONE WRONG

Explanation / Answer

(a) P = F * v = 6.0kg * 9.8m/s² * 2m/s = 117.60 W = 0.117kW

(b) I would find the change in PE and the change in KE.
s = ½at²

1.5 m = ½ * a * (0.42s)² a = 17.00 m/s²
v = at = 17.00m/s2 * 0.42s = 7.142 m/s
KE = ½mv² = ½ * 6.0kg * (7.142m/s)² = 153.06 J
PE = mgh = 6.0 kg * 9.8m/s² * 1.5m = 88.2 J
Power = (153.06J + 88.2J) / 0.42s = 574.42 W

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