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

Energy, work and power — practice question

A car with mass $1250\,\text{kg}$ is travelling along a straight road.
(a(i))[2]

On a horizontal stretch of road, the car is moving at a steady speed of $32\,\text{m s}^{-1}$ and a constant resistive force of $750\,\text{N}$ opposes the motion. Calculate, in kW, the power developed by the car’s engine.

(a(ii))[3]

If this power is suddenly reduced by $8\,\text{kW}$, determine the car’s instantaneous deceleration.

(b)[5]

On a part of the road inclined at $\sin^{-1} 0.096$ to the horizontal, the resistive force on the car is $(1000 + 8v)\,\text{N}$ when its speed is $v\,\text{m s}^{-1}$. The car moves up this slope at constant speed while the engine operates at $60\,\text{kW}$. Find the constant speed.

Worked solution & mark scheme

This 10-mark question has a full step-by-step worked solution and mark scheme. One marking point: Driving force correctly found as $DF=750$

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