- #1

grooveactiva

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## Homework Statement

This is an actual practice problem. I am having trouble understanding the calculations to get to the answer. Your job is to lift 30-kg crates a vertical distance of 0.90 m from the ground onto the bed of a truck.

a) How many crates would you have to load onto the truck in 1 minute for the average power output you use to lift the crates to equal 0.50 hp?

b) How many crates for an average power output of 100 W?

## Homework Equations

Work = mgh.

Power P

_{av}= ΔW/Δt

1 hp = 746 watts

## The Attempt at a Solution

(part a)[/B]Maybe I am reading the problem wrong.

0.50 hp = 746 watts/2 = 373 watts.

Work to lift one crate = W = mgh = (30 kg)(9.81 m/s

^{2})(0.9 m) ~ 265 Joules = 265 watts seconds. So, work in one minute = 60 seconds is (373 W * 60 seconds/minute)/(265 watts seconds per crate) = 84.5 crates in one minute.

Does this make sense as far as calculations are concerned?

**4. The attempt at a solution (part b)**

For 100W of average power output, (100 watts * 60 s)/(265 watts s per crate) = 22.6 crates in one minute.