Frequency Questions

Question

A stroboscope is set to flash every 8.00 X 10^-5 s. What is the frequency of the flashes?

 

 

Find the frequency of a tuning fork that takes 2.50 X 10^-3s to complete one oscillation.

 

 

A tire has a tread pattern with a crevice every 2.00 cm. Each crevice makes a single vibration as the tire moves. What is the frequency of these vibrations if the car moves at 30.0 m/s?

Answer 1

The key is that frequency is the inverse of the period.  (f = 1/T).  Period is the time it takes for one cycle to complete.  So the first two questions can be answered by finding 1/T (one divided by the period).

 

For the third question:  The car moves at 30 m/s.  This is the same as 3000 cm/s.  As the car moves, the tire surface rolls, covering the same distance that the car moves.  The tire has a tread pattern with a crevice every 2 cm.  Since the car is moving at 3000 cm/s, this crevice hits the road 3000/2=1500 times every second.  (In one second, the tire rolls 3000 cm.  Since the crevice hits every 2 cm, this happens 3000/2=1500 times per second.)  The units of frequency are "per second."  Therefore, the frequency is 1500 Hz.