Question

A cannon ball has a mass of 2 kg is fired at a target of 500 meters away. The 400 kg cannon recoils by 50 cm. Assuming cannon ball moves with constant velocity, when will it hit the target? (Resistance offered by ground to cannon is 100 N)

• A. 5 sec
• B. 10 sec
• C. 15 sec
• D. 2 sec

Answer 1

The correct option is A

5 sec

Force by ground on the cannon = 100 N

Work done by ground on the cannon = 100 $\times$ (0.5) = 50J

Applying conservation of energy,

Work done by ground on canon = Kinetic energy of canon immediately after firing = ( $\frac{1}{2}$) m $v^2$​ = 50J

Velocity of cannon (v) = 0.5 $\frac{m}{sec}$

By applying law of conservation of momentum,

(400 $\times$ (0.5) = 2 $\times$ (velocity of cannon ball)

Velocity of canon ball = 100 $\frac{m}{sec}$

Time taken by the canon ball to hit = $\frac{500}{100}$ = 5 seconds