Define power as the rate at which work is done.
Mechanical power $P$ may be found from $P = Fv$. Use the ideas of work and the definition of power to derive this expression.
A lorry engine delivers $130\,\text{kW}$ to the lorry’s wheels while the lorry is moving at a steady $25\,\text{m s}^{-1}$ along a level straight road. Show that the resistive force acting against the lorry’s forward motion is $5200\,\text{N}$.
Determine an expression, in terms of $m$, $g$ and $\theta$, for the part of the lorry’s weight that acts parallel to the road surface.
The resistive force is still $5200\,\text{N}$, and the engine must now supply more power to keep the speed at $25\,\text{m s}^{-1}$. The lorry has total mass $m$ of $36\,000\,\text{kg}$. The angle $\theta$ is $1.4^\circ$. Determine the power, in $\text{kW}$, now delivered by the engine.