Question

A boy fires a gun and hears the echo 2 second later . if he is 350 m away from a wall , calculate the velocity of sound in air.

Answer 1

initial velocity (u) = 0m/sec
final velocity (v) = ?
time taken (t) = 2sec
distance (s) = 350m

we know,, from 2nd equation of motion

s = ut + 1/2 a(t) square
350 = 0 X 2 + 1/2 a(2)square
350 = 0 + 1/2 X a(4)
350 = 0 + 1/2 X 4a
350 = 0 + 2a (2 and 4 was cancelled with 2's table)
350 = 2a
350/2 = a
a = 175m/s2

Now we know the value of acceleration (a)

therefore,,, from 1st equation of motion

v = u + at
v = 0 + 175 X 2
v = 0 + 350
v = 350 m/s

Answer 2

Speed = 350 m/s

Distance travelled by sound = 350+350 m = 700 m

Time taken = 2 sec

Speed = distance/ time = 700/2 = 350m/s