Answer to Question #143686 in Physics for Sydney

Question

A 1.75 kilowatt winch is used to raise loads of bricks up a 24.0 meter building. If the bricks need to get to the top of the building in 2.00 minutes, what is the maximum allowable mass of a load of bricks?

Answer 1

We will try to solve the problem in a reverse order by asking and answering the following questions.

1) How does work depend on mass and height?

$$W=mgh$$

2) Can work be expressed in terms of power and time? Yes:

$$W=Pt.$$

3) Are these values equal? That is, is the work performed by the winch equals the work required to lift the bricks? Yes, so:

$$mgh=Pt,\\\space\\ m=\frac{Pt}{gh}=892\text{ kg}.$$