Free and forced oscillations and resonanceEdexcel International A Level Physics: Flashcards

Exam questions on Free and forced oscillations and resonance

1. A student hangs a mass of 0.250 kg from a spring of spring constant 40 N m⁻¹. She pulls the mass down a short distance and releases it, so that it oscillates. She then attaches the top of the spring to a vibration generator whose frequency can be varied while its amplitude is kept constant.
   Calculate the natural frequency of the mass–spring system.2 marks
2. A loose plastic panel in a car dashboard rattles violently when the engine speed reaches 3000 revolutions per minute, but hardly at all at other engine speeds. The engine vibrations act as a periodic driving force on the panel.
   Suggest how the rattling of the panel could be reduced without changing its natural frequency.2 marks
3. A steel strip is clamped at one end and has a natural frequency of 12 Hz. A vibration generator drives the strip at constant driving amplitude, and the driving frequency is increased from 5 Hz to 20 Hz. The investigation is repeated after a large card has been fixed to the free end of the strip, which increases the air resistance on the strip.
   Describe how the amplitude of oscillation of the strip varies as the driving frequency is increased from 5 Hz to 20 Hz, without the card.3 marks