Question

A projectile is fired from the top of a 40 m high cliff with an initial speed of 50 m/s at an unknown angle. Find its speed when it hits the ground

• A. 45 m/s
• B. 58 m/s
• C. 38 m/s
• D. None of these

Answer 1

The correct option is B

58 m/s

Lets apply concepts of work energy while the ball is in air. Only gravitational force acting on it, which is conservative, so we can conserve mechanical energy.

$U_{initial}$ + $K_{initial}$ = $U_{final}$ + $K_{final}$

mg 40 + $\frac{1}{2}m(50{)}^2=0+\frac{1}{2}m{v}^2$

$v^2$ = 800 + 2500

$v^2$ = 3300

v = 58 m/s