Question

A certain instant camera determines the distance to the subject by sending out a sound wave and measuring the time needed for the wave echo to return to the camera. how long would it take the sound wave to return to the camera if the subject were 3.42 m away? the speed of sound is 343 m/s. answer in units of s.

Answer 1

The total distance covered by the sound wave is twice the distance between the camera and the subject (because the wave has to reach the subject and then travel back to the camera), so 2L, where L=3.42 m. The speed of sound is v=343 m/s. It is a uniform linear motion, so we can use the basic relationship between space (S), time (t) and velocity (v) to find the time the wave needs to return to the camera:
$t= \frac{S}{v}= \frac{2L}{v}= \frac{2\cdot 3.42 m}{343 m/s}=0.020 s$