Question

A projectile is fired from the top of a cliff of height $1000m$ with a speed of $40m{s}^{-1}$ at an unknown angle. The speed of projectile when it hits the ground is (take $g=10m{s}^{-2}$, Neglect air friction)

• A. $60m{s}^{-1}$
• B. $40m{s}^{-1}$
• C. $100m{s}^{-1}$
• D. $200m{s}^{-1}$

Answer 1

The correct option is A $60m{s}^{-1}$


Applying conservation of energy principle, $[A\to B]$
$U_i+K_i=U_f+K_f\Rightarrow \frac{1}{2}m[40{]}^2+mg[1000]=\frac{1}{2}m{v}^2+0\Rightarrow 800m+1000m=\frac{1}{2}m{v}^2\Rightarrow v^2=3600\Rightarrow v=60m{s}^{-1}$