Question

Two trucks heading in opposite directions with speed of 60kmph and 70kmph respectively, approach each other.The driver of the first truck sounds his horn of frequency of 400Hz.What frequency does the driver of the sound truck hear?(velocity of sound =330m/s).After the two trucks have passed each other,what frequency does the driver of second truck hear.?

Answer 1

Answer:

465.18hz

Explanation: convert velocity of source and observer into m/s.we get source vel=60×5/18m/s

obs vel=70×5/18m/s

we know as both source and observer are approaching each other

apparent frequency

n=N(V+u/V-v)

N-original frequency.V-sound velocity,u-source velocity,v-observer velocity.

(we should remember that this formula is valid only when source and observer are moving towards each other.)

n=400((330+70×5/18)/(330-60×5/18))

=465.81hz