A roller coaster uses contact-free magnetic brakes near the end of its track. Fig. 1 shows an aluminium fin attached to the car moving between the poles of ...
Question 1 Report
A roller coaster uses contact-free magnetic brakes near the end of its track. Fig. 1 shows an aluminium fin attached to the car moving between the poles of a magnet. As the fin enters the magnetic field, currents are induced in the metal. The braking system has no wires connected to the moving car and no battery in the brake unit.
(a) State the direction of the force produced by the magnetic brake compared with the direction of motion of the car. [2]
(b) Explain how an induced current is produced in the aluminium fin. [3]
(c) Explain why the induced current produces a force that slows the car. [3]
(d) Describe how the braking effect changes as the speed of the car decreases. [2]
(e) Calculate the kinetic energy of a 600 kg car travelling at 12 m/s as it enters the brake section. [3]
(f) State the main energy transfer as the car slows down. [2]
(g) Give two advantages of this magnetic brake compared with a brake using rubbing pads. [2]
Answer Details
(a) The braking force acts opposite to the car's motion, so it slows the car. [2]
(b) The aluminium fin moves through the magnetic field. This changes the magnetic flux through parts of the fin and induces eddy currents in it. [3]
(c) The induced current produces its own magnetic field. By Lenz's law, this field opposes the change causing it, namely the fin entering the field. The magnetic interaction therefore produces a force opposite to the motion. [3]
(d) The braking force decreases as the car slows. At lower speed, the magnetic flux changes less rapidly, so the induced current is smaller. [2]
(e) \[E_k=\frac12mv^2=\frac12\times600\times12^2=43200\text{ J}=4.32\times10^4\text{ J}\] [3]
(f) The car's kinetic energy is transferred mainly to thermal energy in the aluminium fin and magnet system. Some is also transferred as sound. [2]
(g) Magnetic braking has no rubbing contact, so there is less wear and less maintenance. It also gives smooth braking and can work in wet conditions. [2]
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