Physics 9702 · AS & A Level · Gravitational potential energy and kinetic energy

Gravitational potential energy and kinetic energy — practice question

A car with mass $1500\,\text{kg}$ is moving along a straight horizontal road at constant velocity $v$. A total resistive force $F$ acts on the car, as illustrated in Fig. 3.1.
(a)[2]

Show that the engine power required to overcome the total resistive force is expressed by the equation $P = Fv$.

(b)

The car then travels up a slope at constant speed of $30\,\text{m s}^{-1}$. The slope makes an angle of $6.0^{\circ}$ to the horizontal, as shown in Fig. 3.2. The total resistive force on the car is $1600\,\text{N}$.

(b(i))[2]

Show that, in $1.0\,\text{s}$, the car’s increase in gravitational potential energy is $46\,000\,\text{J}$.

(b(ii))[2]

Use the result from (b)(i) to determine the engine power needed to move the car up the slope.

(c(i))[1]

The car takes on a passenger and then goes on up the slope at the same speed as in (b). State and explain any effect the passenger has on the air resistance acting on the car.

(c(ii))[1]

State and explain the effect, if any, that the passenger has on the power developed by the engine.

Worked solution & mark scheme

This 8-mark question has a full step-by-step worked solution and mark scheme. One marking point: Expression for work done, $W = Fd$

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