Question

A pebble is thrown vertically upwards from a bridge with an initial velocity of $4.9m{s}^{-1}$. It strikes the water after $2s$. Height of the bridge is:

• A. $19.6$ m
• B. $14.7$ m
• C. $9.8$ m
• D. $4.9$ m

Answer 1

The correct option is C $9.8$ m

Option C is correct
$s=ut+\frac{1}{2}a{t}^2$
$u=+4.9m/s$
$g=-9.8m/s^2$
$t=2sec.$
$\Rightarrow s=4.9\times 2-\frac{1}{2}\times 9.8\times (2{)}^2=-9.8m$
Height is $|s|=9.8m$