Physics - Kinematics Question with Solution | TestHub

To find the height of the bridge ($h$) and the final velocity ($v$), we use kinematic equations.

Given:

Initial velocity, $u=+4.9m/s$ (upwards is positive)

Time, $t=2s$

Acceleration due to gravity, $g=-9.8m/s^2$ (downwards is negative)

Height of the bridge:

Using $s=ut+\frac{1}{2}g{t}^2$:

$h=(4.9)(2)+\frac{1}{2}(-9.8)(2{)}^2$

$h=9.8-19.6$

$h=-9.8m$

The negative sign indicates the displacement is downwards from the bridge. So, the height of the bridge is $9.8m$.

Final velocity:

Using $v=u+gt$:

$v=4.9+(-9.8)(2)$

$v=4.9-19.6$

$v=-14.7m/s$

The negative sign indicates the velocity is downwards. So, the pebble strikes the water with a speed of $14.7m/s$.

Therefore, the height of the bridge and the velocity with which the pebble strikes the water are $9.8m$ and $14.7m/s$ respectively.

The final answer is $\boxed{B}$.