CAIE IGCSE Physics 1.7.2 Work Topic Practice

A train of mass $1.8 \times 10^{5} \mathrm{~kg}$ is at rest in a station. At time t=0, the train begins to accelerate along a straight, horizontal track and reaches a speed of $20 \mathrm{~m} / \mathrm{s}$ at $t=15 \mathrm{~s}$. The train continues at a speed of $20 \mathrm{~m} / \mathrm{s}$ for 10 s.

At $t=25 \mathrm{~s}$, the driver applies the brakes and the resistive force on the train causes it to decelerate uniformly to rest in a further 24 s.

Fig. 4.1 is an incomplete distance-time graph for this journey.

While the train decelerates to rest, it does work against the resistive force and its kinetic energy decreases.

Define work done.

A car accelerates uniformly in a straight line from rest at time t=0. At $t=3.2 \mathrm{~s}$, the speed of the car is $13.0 \mathrm{~m} / \mathrm{s}$.

The car decelerates from $13.0 \mathrm{~m} / \mathrm{s}$ to $0 \mathrm{~m} / \mathrm{s}$ at a constant deceleration. The mass of the car is 1350 kg . The car travels 13 m in 2.0 s as it decelerates.

Show that the work done by the car as it decelerates is approximately $1.1 \times 10^{5} \mathrm{~J}$.

Fig. 2.1 shows a wooden trolley of mass 1.2 kg at rest on the rough surface of a bench.

A ball of mass 0.52 g travels horizontally towards the trolley. The ball embeds itself in the wood of the trolley. The trolley moves with an initial speed of $0.065 \mathrm{~m} / \mathrm{s}$.

As the trolley moves across the rough surface, it slows down and stops.

Explain, in terms of the work done, the energy change that takes place as the trolley slows down.