Forced vibrations, resonance and dampingAQA A-Level Physics: Flashcards

Exam questions on Forced vibrations, resonance and damping

1. A child sits on a playground swing. When pushed once and left alone, the swing oscillates freely with a natural frequency of 0.50 Hz. A parent then pushes the swing at regular intervals, applying a small force each time.
   Explain why the amplitude of the swing becomes very large when the parent pushes at 0.50 Hz.2 marks
2. A pedestrian footbridge has a natural frequency of 2.0 Hz for its vertical oscillations. When a large crowd crossed it on opening day, the bridge began to sway noticeably. Engineers have since fitted dampers containing viscous oil to the underside of the deck.
   Explain how the oil dampers make the bridge safer when large crowds cross it.2 marks
3. A tuning fork of frequency 512 Hz is held over the open end of a long glass tube that is closed at the bottom by water. The water level can be lowered to change the length of the air column. The speed of sound in air is 340 m s⁻¹ and end effects may be ignored.
   The air column resonates strongly when the length of the column is a certain value. Explain how a stationary wave is formed in the tube and why resonance occurs.3 marks