Energy, work and power

As shown in Fig. 3.1, water is heated by two different kettles. The picture includes an electric kettle and a gas-heated kettle with a gas burner. The information for both kettles is given in Fig. 3.2.

May/June 2015

Wind energy is a renewable energy source. A wind turbine and generator convert the energy in the wind into electrical energy. Fig. 9.1 shows some wind turbines.

May/June 2018

As illustrated in Fig. 3.1, a battery, a pulley and a motor are used to raise a load.

May/June 2025

Fig. 2.1 presents a fork-lift truck being used to raise a load. While the load is being lifted, the electric motor on the fork-lift truck has a useful output power of 600 W.

May/June 2025

Fig. 9.1 displays a large container ship moving in a straight line at constant speed. The resistive force on the ship is $2.8 \times 10^{6}\,\text{N}$.

Oct/Nov 2017

A filament lamp rated at 75 W in an office is mistakenly left on for 63 hours while the office is shut.

Oct/Nov 2017

An electrical heater has a power of $3.0\,\text{kW}$. It is left on for $2\,\text{hours}\,30\,\text{minutes}$. The charge for running the heater for this period is $120\,\text{c}$. What is the price of $1.0\,\text{kWh}$ of electrical energy?

Oct/Nov 2018

A motor is employed to raise a load through a vertical distance of $0.50\,\text{m}$, as illustrated. The load has a weight of $40\,\text{N}$. The motor has a power rating of $20\,\text{W}$ and the system operates at $25\%$ efficiency. How long does it take to raise the load?

Oct/Nov 2018

The combined mass of the wheelbarrow and its load is 90 kg. A worker pushes the wheelbarrow and load up a plank of length $2.0\,\text{m}$ onto a platform. The platform is $0.60\,\text{m}$ above the ground. The worker applies a force of $290\,\text{N}$ to the wheelbarrow in the same direction as its motion.

Oct/Nov 2020

A trolley with mass 0.20 kg is initially at rest on a surface with no friction. A block of wood is fixed to the trolley. The block of wood has volume 0.0012 m$^3$, and the wood has density 650 kg m$^{-3}$.

Oct/Nov 2024

In a factory, an electric motor is used to raise the boxes shown in Fig. 2.1. Diagram labels: motor, power supply, cable, boxes, cage. The boxes sit inside a cage, and the motor coils a cable round a cylinder to lift the cage and boxes. The combined mass of the boxes is 37 kg and they are lifted straight up through 13 m to a storage area.

Oct/Nov 2025

A spherical container carries measuring instruments down to the bottom of a lake. Figure 2.1 shows the container at rest just beneath the water surface of a lake. Diagram labels: water surface, container. The container is let go and sinks through the water to the lake bottom. It moves a vertical distance of 32 m before striking the bottom of the lake. The combined mass of the container and instruments is 74 kg.

Oct/Nov 2025

A student is assessing the efficiency of a small electric heater. Fig. 1.1 shows a circuit containing a d.c. power supply, ammeter, switch and a coil of wire (small electric heater) in a 100 cm^3 beaker. In (b)(i), the student is also given a thermometer, a stirrer, a measuring cylinder containing water at room temperature and a stopwatch.

Oct/Nov 2025