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Energy Transfer

What is the Difference between Power and Energy?

The equation that connects power and energy is

Power = Energy ÷ Time.

This equation is important!

Power is the rate at which energy is transferred.
Power is measured in Watts. 1 Watt = 1 Joule per second.

What is the Power Output of a Motor?

Q.   A motor lifts a 15 kg mass by 3 metres in 8 seconds.
What is the motor's power output ?

A.  The motor has transferred rotational energy
into gravitational potential energy.

GPE = mass x gravity x height.

= 15 x 10 x 3 
= 450 J.        

When the 15 kg mass is 3 metres high it has
gained 450 J of gravitational potential energy.
It has gained this energy in 8 seconds.

Power = Energy ÷ Time

= 450 ÷ 8
    = 56·25 W.

The motor's power output is 56·25 Watts.

There is also an equation for power in electricity.

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