Question

A scooter waiting on a signal has its mirror vibrating violently. Why?

• A. As the natural frequency of the mirror matches with that of the mirrors of other cars on the signal
• B. As the natural frequency of the mirror matches with that of the engine of the scooter
• C. As the natural frequency of the mirror matches with the frequency of the scooter
• D. As the rough road causes the mirror to vibrate violently
• E. As the mirror is undergoing natural vibration

Answer 1

The correct option is B

As the natural frequency of the mirror matches with that of the engine of the scooter

This is because of resonance. When a body is subjected to forced vibration with a frequency which equal to or an integral multiple of the natural frequency of the body, the body vibrates with large amplitude violently. The mirror has a natural frequency equal to or multiple of frequency of the engine of the scooter (frequency of forced vibration) & hence it is vibrating violently. The rider should switch of the engine or change the speed of the scooter.