Question

The splash sound is heard 3 seconds after a stone is dropped from a bridge. Find the height of the bridge from the level of river water. [Take g=9.8 metre per second square] 


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Answer 1

QUESTION:-

The splash sound is heard 3 seconds after a stone is dropped from a bridge. Find the height of the bridge from the level of river water. [Take g=9.8 m/s²]

EXPLANATION:-

Let the time taken to touch=T

and when sound cones=t   [REMEMBER THAT T and t are different]

So,

T+t=3

T=3-t   (EQ-1)

Now,

We know that,

s = ut + 1/2 × at²

s = 0(t) + 1/2 × 9.8 × t²

s = 0 + 4.9t²

s = 4.9t²

We know that,

Speed of sound in air is 340 m/s

We also know,

Speed=distance/times

So, time will be,

Time=Distance/time

T = 4.9t²/340

3 - t = 4.9t²/340

340(3 + t) = 4.9t²

1020 - 340t = 4.9t²

1020 - 340t - 4.9t² = 0

4.9t² + 340t - 1020 = 0

LET'S USE QUADRATIC FORMULA:-

x = -b ± √b² - 4ac/2a

x = -340 ± √(340)² - 4(4.9)(-1020)/2(4.9)

x = -340 ± √115600 - (-19992)/9.8

x = -340 ± √1,35,592/9.8

x = -340 ± 368.2/9.8

x = 2.8

s = 4.9 t²

s = 4.9 × (2.8)²

s = 4.9 × 7.84

s = 38.4 m

Answer 2

Answer:

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Explanation:

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