# Work And Power Problem

1. Dec 21, 2004

### DethRose

Hey i have another work and power problem that i have no idea what to do on

this one states

a conveyor belt is driven by a motor rated at 35 kW. Only 73% of the rated power is available to do useful work. The coal is to be raised and deposited into a hopper 21.1 m above. How many kilograms of coal can be delivered per minute.

i found that the motor is 25.55 kW at 73% but thats as far as i got lol

help please

2. Dec 21, 2004

### NateTG

How much energy does it require to move 1 kg of coal up 21.1 m?

3. Dec 21, 2004

### dextercioby

Power is work/time=force*velocity.From here u can say that
$$P=\frac{F\cdot h}{t}=\frac{mg\cdot h}{t}\Rightarrow \frac{m}{t}=\frac{P}{gh}$$
The rate (mass carried per second) is:
$$\frac{25550W}{9.80665ms^{-2} 21.1m} approx.=123Kg/s$$

I'll let u compute the mass carried in one minute.

Daniel.

Last edited: Dec 21, 2004
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