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Dropping Objects

A stone is dr...

Question

A stone is dropped from a bridge and it reaches the ground in $4$ seconds. The height of the bridge is

A

78.4 m

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B

64.2 m

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C

98.6 m

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D

116.8 m

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Solution

The correct option is A $78.4 m$
From the question, it is clear that $u = 0$
Time to reach the ground is $t = 4 s e c$
Applying $2^{n d}$ law of motion for constant acceleration, we have
$s = u t + \frac{1}{2} a t^{2}$
$\Rightarrow h = 0 + \frac{1}{2} \times 9.8 \times (4)^{2} = 78.4 m$
Hence, height of the bridge is $h = 78.4 m$

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