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

Energy, work and power — practice question

A car with mass $1500\,\text{kg}$ is moving along a straight, level road.
(a)[4]

A constant resistive force acts against the motion. The car engine is producing $24\,\text{kW}$ while the car moves at a steady $32\,\text{m s}^{-1}$. The power is then raised to $28\,\text{kW}$. Determine the car’s acceleration at the moment when its speed is $36\,\text{m s}^{-1}$.

(b)[3]

Instead, the resistance to the motion of the car is $(340 + 4v)\,\text{N}$ when the car moves with speed $v\,\text{m s}^{-1}$. With the engine operating at $20\,\text{kW}$, the car travels at constant speed. Determine this constant speed.

Worked solution & mark scheme

This 7-mark question has a full step-by-step worked solution and mark scheme. One marking point: Resistive force $R=\tfrac{24000}{32}=750$.

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