Question

A stone is thrown with an initial speed of 4.9 m $s^{-1}$ from a bridge in the vertically upward direction. It falls down in water after 2 s. The height of the bridge is :

• A. 24.7 m
• B. 19.8 m
• C. 9.8 m
• D. 4.9 m

Answer 1

The correct option is C 9.8 m

Initial velocity of the stone $u=-4.9m/s$ (upwards)

Acceleration of the stone $g=9.8m/s^2$ (downwards)

Time taken by the stone to fall down in water $t=2$ s

Height of the bridge $H=ut+\frac{1}{2}g{t}^2$ (Taking downward direction to be positive)

$\therefore$ $H=(-4.9)\left(2\right)+\frac{1}{2}\left(9.8\right)(2{)}^2=9.8$ m