How many crates can you load in a minute with different average power outputs?

[grooveactiva]

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/s²)(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.

 

[BvU]

Does this make sense as far as calculations are concerned?

Yes
Pretty powerful, them horses, eh ?