Question

To estimate the height of a bridge over a river, a stone is dropped freely on the river from the bridge. The stone takes 2s to touch the water surface in teg river. Calculate the height of the bridge from the water level. Take g=9.8m/s²​

Answer 1

Explanation:

Given

T=2s

We know that

u=0m/s

T=2s

g=9.8m/s²

To solve the question note the formula

ut+1/2at²=S

1/2at²=S

1/2*9.8m/s²*4s²=S

19.6m=Height of bridge over river

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Answer 2

Question:

To estimate the height of a bridge over a river, a stone is dropped freely on the river from the bridge. The stone takes 2s to touch the water surface in teg river. Calculate the height of the bridge from the water level. (Take g=9.8m/s²)

Solution:

Given:

• initial velocity ( u ) = 0m/s

[ Whenever a body is dropped freely from a height then, u = 0]

• time take ( t ) = 2s

To find:

• height of the bridge ( h )

Calculation:

We know,

$\sf\red { h = ut + \dfrac{1}{2}g{t}^{2}}$

Substituting values-

$:\implies \sf { h = 0 \times 2 + \dfrac{1}{2} \times 9.8 \times 2 \times 2}$

$\:$

$:\implies \sf { h = 0 + \dfrac{1}{\cancel2} \times 9.8 \times \cancel2 \times 2}$

$\:$

$:\implies \sf { h = 0 + 1 \times 9.8 \times 2}$

$\:$

$:\implies \sf\red { h = 19.6 m( Approx) }$

$\therefore$ The height of the bridge from the water level is 19.6m.

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