# John uses a pulley to lift the sail on his sailboat. The sail weighs 150 N, and he must lift it 4.0 m. The pulley is 50% efficient. How much work must be done to lift the sail? How much work must John do on the rope to lift the sail?

##### 1 Answer

#### Answer:

See below:

#### Explanation:

In order to lift the sail upward 4 meters, John must increase its Gravitational potential energy by doing work against gravity (i.e hoisting the sail).

We are given the weight of the sail due to gravity,

Using the formula for Gravitational potential energy.

This is how much work must be done to lift the sail 4 meters. However, using a pulley, like John's, it is only 50% efficient. I assume this would mean John would have to put in twice as much energy,

However, efficiency is a measure of **output power/input power**, So my assumption might not be entirely correct. Power is energy over time- and we are not given the time it takes for John to hoist the sail.