# Relation Between Power and Velocity

by • 04/07/2012 • GeneralComments (0)508

## Power

Power is defined as the rate of doing work.

If work ΔW is done in time Δt by a body, then its average power is given by P(av) = ΔW / Δt

Power of an agency at a certain instant is called instantaneous power.
Relation Between Power and Velocity

Suppose a constant force F moves a body through a displacement Δd in time Δt, then

P = ΔW / Δt

P = F . Δd / Δt ………………… {since ΔW = F.Δd}

P = F . Δd / Δt

P = F . V …………………………… {since Δd / Δt = V}

Thus power is the dot product of force and velocity.
Units of Power

The unit of power in S.I system is watt.

P = ΔW / Δt = joule / sec = watt

1 watt is defined as the power of an agency which does work at the rate of 1 joule per second.

Bigger Units → Mwatt = 10(6) watt

Gwatt = 10(9) watt

Kilowatt = 10(3) watt

In B.E.S system, the unit of power is horse-power (hp).

1 hp = 550 ft-lb/sec = 746 watt

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