Physics 9702 · AS & A Level · Damped and forced oscillations, resonance
Damped and forced oscillations, resonance — practice question
A bar magnet with mass $180\ \text{g}$ is hung from the free end of a spring, as shown in Fig. 2.1. It is positioned so that one pole lies close to the centre of a wire coil. The coil is connected in series with a resistor and a switch, and the switch is open. The magnet is moved vertically and then released so that it oscillates, with one pole still inside the coil while the other remains outside it. At time $t = 0$, the magnet is moving freely as it passes through its equilibrium position. At time $t = 3.0\ \text{s}$, the switch in the circuit is closed. Fig. 2.2 shows how the vertical displacement $y$ of the magnet varies with time $t$.
(a)[2]
Determine, to two significant figures, the magnet's oscillation frequency.
(b)[1]
State whether closing the switch leads to light, heavy or critical damping.
(c)[6]
Calculate the change in the energy $\Delta E$ of oscillation of the magnet between time $t = 2.7\ \text{s}$ and time $t = 7.5\ \text{s}$. Show your working.
Worked solution & mark scheme
This 9-mark question has a full step-by-step worked solution and mark scheme. One marking point: “period read from the graph, e.g. $T = \frac{3}{2.5}$” …