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Physical World

Question

A stone is thrown with an initial speed of 4.9m/s from a bridge in vertically upward direction.It falls down in water after 2sec. The height of bridge is

24.7m

19.8 m

9.8 m

4.9 m

Solution

9.8 m

Here :- Initial velocity u=-4.9m/s (-ve is due to vertically upward motion)

Total time t = 2sec

The height of the bridge is given by

s =ut+ $\frac{1}{2} {at}^{2}$

Here we consider a=g $\Rightarrow$ acceleration due to gravity

$s = - 4.9 \times 2 + \frac{1}{2} \times 9.8 \times {(2)}^{2} = - 9.8 + 19.6 = 9.8 m$