A horizontal bridge is built across a river. A student standing on the bridge throws a small ball vertically upwards with a velocity $4m{s}^{- 1}$ .
The ball strikes the water surface after $4s$ . The height of bridge above water surface is
(Take $g = 10m{s}^{- 2}$ ):

Question

A horizontal bridge is built across a river. A student standing on the bridge throws a small ball vertically upwards with a velocity

4m{s}^{- 1}

.
The ball strikes the water surface after

4s

. The height of bridge above water surface is
(Take

g = 10m{s}^{- 2}

):

Quantrex Academy · Accepted Answer

Correct answer: D. 64m

The formula to calculate the vertical height travelled by the ball is given by
$H = ut - \dfrac{1}{2}g{t}^{2} . . . \left(1\right)$
Substitute the values of the known parameters into equation (1) to calculate the required height.
$\begin{cases}H & = & 4{ms}^{- 1} \times 4s - \dfrac{1}{2} \times 10{ms}^{- 2} \times {\left(4s\right)}^{2} \\ & = & - 64m\end{cases}$
Hence, the required height of the bridge above the surface of the river is $64m$ .

A horizontal bridge is built across a river. A student standing on...

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