Question

A car approaches a hill with constant speed. When it is at a distance of 0.96 km., it blows horn whose echo is heard by the driver 6 second later. If the speed of sound in air is 300 m/s, calculate the speed of the car.
(Biher./NTSE Stage-1/2017)
(A) 100 m/s
(B) 20 m/s
(C) 50 m/s
(D) 70 m/s

PLEASE GIVE STEP BY STEP EXPLANATION.​

Answer 1

Answer:

option (B) 20 m/s

Explanation:

Distance travelled by engine = v x 6sec =

x m

Distance travelled by sound =960+(960−x) =(1920−x)m ⇒

velocity of sound=300m/s

v = distance/time

300= (1920−x)6

1800=1920−x

x=1920−1800

x=120m

Speed of car = x/5

=120/6

=20m/s

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Answer 2

Answer:

20 m/s

Explanation:

distance travelled by engine=V×6 sec=xm

distance travelled by sound

960+(960-x). (1920-x)m

velocity of sound=300m/s

V=distance/ time

300=(1920-x)6

1800=1920-x

x=1920-1800

x=120

speed of car=x/6

120/6

20 m/s