Question

A projectile is fired horizontally with a velocity of $98\text{m/s}$ from the top of a hill $490\text{m}$ high. Find the time taken by the projectile to reach the ground.

• A. $20s$
• B. $10s$
• C. $25s$
• D. $15s$

Answer 1

The correct option is B $10s$

Here, it will be more convenient to choose x and y directions as shown in figure.
here, $u_x=98m/s,a_x=0,u_y=0$ and $a_y=g$
At A, $s_y=490$ m. So, applying
$s_y=u_{y}t+\frac{1}{2}{a}_y{t}^2$
$\therefore 490=0+\frac{1}{2}\left(9.8\right)t^2$
$\therefore t=10s$