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Physics Wave and Sound Mix MCQ (Single Correct)

An engine approaches a hill with a constant speed. When it is at a distance of 0.9 km it blows a whistle, whose echo is heard by the driver after 5 sec. If speed of sound in air is 330 m/s, the speed of engine is

A
10 m/s
B
20 m/s
C
30 m/s
D
40 m/s

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Text Solution

Verified by Experts
The correct answer is:
C

If the speed of engine is v, the distance traveled by engine in 5 sec will be 5v, and hence the distance traveled by sound in reaching the hill and coming back to the moving driver = 900 + (900 – 5v) = 1800 – 5v.

So the time interval between original sound and it’s echo

⇒ ⇒ v = 30 m/s.

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