Work, Energy & Power

This lesson covers work, energy, and power at A-Level. These concepts provide an alternative approach to solving mechanics problems — instead of using forces and acceleration directly, we use energy methods. This approach is particularly powerful for problems where the force varies or the motion is complex.

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Work Done

The work done by a constant force $F$F moving an object through displacement $d$d in the direction of the force is:

$W = Fd$W=Fd

If the force acts at angle $\theta$θ to the direction of motion:

$W = Fd\cos\theta$W=Fdcosθ

Scenario	Work done
Force in direction of motion	$W = Fd$W=Fd (positive)
Force at angle $\theta$θ to motion	$W = Fd\cos\theta$W=Fdcosθ
Force perpendicular to motion	$W = 0$W=0 (no work done)
Force opposing motion (friction)	$W = -Fd$W=−Fd (negative — energy dissipated)

The unit of work is the joule (J): 1 J = 1 Nm.