# Homework Help: Simple Machines

1. Mar 14, 2004

### pvpanther05

I totally do not understand how to do this. I missed this day in class and the teacher hasn't had time to explain it to me. Could someone help?

The efficiency of a pulley system is 73%. The pulleys are used to raise a mass of 58 kg to a height of 3.0 m. WHat force is exerted on the string of the pulley systen if the string is pulled for 18.0 m in order to raise the mass of the required height?

2. Mar 14, 2004

### ShawnD

The way pullies work is by doing an equivalent amount of work by decreasing the amount of force needed and increasing the distance the force is applied over.
work = work
$$F_1d_1 = F_2d_2$$

Efficiency is always what you get out divided by what you put in. I'll use a little "e" to express efficiency.
e = out/in
e*in = out

Now just fill in values

$$eF_1d_1 = F_2d_2$$

$$(0.73)F_1(18.0) = (58)(9.8)(3)$$

$$F_1 = 129.77$$

Last edited: Mar 14, 2004