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.
(a)[3]
The container reaches terminal velocity before it hits the bottom of the lake. Explain, in terms of the forces acting on the container, how its motion through the water changes until terminal velocity is reached.
(b(i))[2]
Calculate the energy transferred from the container’s gravitational potential energy store.
(b(ii))[2]
State the principle of conservation of energy.
(b(iii))[2]
Work is done to move energy out of the gravitational potential energy store as the container falls at terminal velocity. Describe, in terms of the work done, how the energy is transferred from the gravitational potential energy store to one other energy store in the water.
Worked solution & mark scheme
This 9-mark question has a full step-by-step worked solution and mark scheme. One marking point: “At first, its weight makes it accelerate, or speed up, or gain kinetic energy” …