Question

A pulley system with 76% efficiency is set up to lift a 18kg bag of nails. The bag is lifted to a height of 2.1m by a person pulling on the rope with a force of 58.0N.

1) What is the work done on the bag of nails by the pulley?


2) How much work is input to the system?

Answer 1

Question#18437

A pulley system with 76% efficiency is set up to lift a 18kg bag of nails. The bag is lifted to a height of 2.1m by a person pulling on the rope with a force of 58.0N.

1) What is the work done on the bag of nails by the pulley?

2) How much work is input to the system?

Solution:

Let:

$$m = 18 \text{ kg}$$ $$H = 2.1 \text{ m}$$ $$k = 76\% = 0.76$$

A(pulley) - ?

A(input) - ?

$$A(\text{pulley}) = FH = mgH = 18 * 9.8 * 2.1 = 370.44 \text{ J}$$ $$A(\text{input}) = \frac{A(\text{pulley})}{k} = \frac{370.44}{0.76} = 487.42 \text{ J}$$

Answer: the work by the pulley is 370.44 J, the work input to the system is 487.42 J