Mathematics 9709 · AS & A Level · Energy, work and power

Energy, work and power — practice question

A car with mass $1400\,\text{kg}$ is travelling on a straight road while a constant force of $1250\,\text{N}$ opposes its motion.
(a(i))[2]

Calculate the work done against the resisting force in the first $8\,\text{s}$ as the car travels along a horizontal stretch of road at a steady speed of $36\,\text{m s}^{-1}$.

(a(ii))[2]

Calculate the engine power developed by the car, in kW.

(a(iii))[3]

If this power is then increased suddenly by $12\,\text{kW}$, find the instantaneous acceleration of the car.

(b)[2]

The car now moves at a steady speed of $32\,\text{m s}^{-1}$ up a road section inclined at $\theta^\circ$ to the horizontal, with the engine operating at $64\,\text{kW}$. Find the value of $\theta$.

(iii)[3]

If this power is then increased suddenly by $12\text{ kW}$, find the instantaneous acceleration of the car.

Worked solution & mark scheme

This 12-mark question has a full step-by-step worked solution and mark scheme. One marking point: Use $\text{Work Done} = \text{Force}\times\text{Distance}$ to write $WD=1250\times36\times8$

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