 # Power

 From: Jason Li Date: 16 Feb 1999 Subject: Is there a difference between Force and Power? I can't even do the first question of my mechanics homework, which is to do with power: A truck of mass 2800kg is accelerating along a straight road at 2.5 m s-2 Resistance forces amount to 1200N. Calculate the power developed by the engine at the instant when the lorry is travelling at 10m/s. I think that the force developed by the engine is 8200 Newtons. Is this the same as the power, or not?

### Maths Help suggests:

Power and Force are not the same thing.

Power is the rate at which work is done.

Power, for constant forces, is calculated using providing that the velocity is in the same direction as the force.

To analyse this problem, draw a diagram: Applying Newton's 2nd Law ("F=ma") gives
F - 1200 = 2800×2.5
from which F = 8200

In your case, the Force is indeed 8200N.
To work out the power, multiply by the velocity of 10 m/s to give 82000 Watts, or 82kW

Return to the Mechanics subject list, or read on for a more detailed explanation...

We know "Work Done = Force × Distance", or Power is the rate of doing work, so And if the force is constant, this simplifies to which leads to the formula as before.