Question

A car approaches a hill with a constant speed. When it is at a distance of 0.96 km, it blows horn whose Eco is heard by the driver 3 second later. If the speed of the sound in air is 300 m/s. Then calculate the speed of the car.​

Answer 1

Answer:

this is the answer

Explanation:

A

100 m/s

B

20 m/s

C

50 m/s

D

70 m/s

Answer

B

Solution

Here, t = 6 s and speed of sound vs=300m/s

Now, distance travelled by the car = v×6=x

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

Since, vs=st

or 330=(1920−x)6or1800=1920−x

x = 120 m

Speed of car, v=x6=1206=20m/s

Answer 2

Given

• A car approachs a hill with a constant speed.
• At a distance, 0.96 km, a horn is blowed.
• The echo of the horn is heard by the driver 3 seconds later.
• Speed of the sound in air = 300 m/s

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To Find

• The speed of car

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Solution

Speed of engine (v) = v

Time taken (t) = 3 seconds

Distance travelled = Speed × Time

⇒ v × 3

⇒ 3v = x m

Distance at which the horn is blowed = 0.96 km = 960 m

Distance travelled by sound = 960 + (960 - x)

⇒ 960 + 960 - x

⇒ 1920 - x m

Speed of sound (v) = 300 m/s

Distance = Speed × Time

⇒ 1920 - x = 300 × 3

⇒ 1920 - x = 900

⇒ -x = 900 - 1920

⇒ - x = -1020

⇒ x = 1020 m

Speed of the car = Distance ÷ Time

⇒ v = 1020 ÷ 3

⇒ v = 340 m/s

∴ The speed of the car is 340 m/s.

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