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

Gravitational potential energy and kinetic energy — practice question

A cyclist is travelling up a slope with a constant gradient. The cyclist takes $8.0\,\text{s}$ to climb the slope. Figure 3.1 shows how the cyclist’s speed $v$ varies with time $t$.
(a)[3]

Use Fig. 3.1 to find the total distance travelled up the slope.

(b)

The bicycle plus the cyclist has a combined mass of $92\,\text{kg}$. The cyclist moves through a vertical height of $1.3\,\text{m}$.

(b(i)1)[2]

For the bicycle and cyclist during the interval from $t = 0$ to $t = 8.0\,\text{s}$, use Fig. 3.1 to calculate the change in kinetic energy.

(b(i)2)[2]

Calculate the change in gravitational potential energy for the cyclist.

(b(ii))[2]

The cyclist pedals continuously so that the useful power delivered to the bicycle is $75\,\text{W}$. Calculate the useful work done by the cyclist while climbing the slope.

(c(i))[1]

Some energy is spent overcoming frictional forces. Use your answers in (b) to show that the total energy converted in overcoming frictional forces is about $670\,\text{J}$.

(c(ii))[1]

Determine the mean magnitude of the frictional force.

(d)[2]

Suggest why the total resistive force does not remain constant in magnitude.

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