Question

A ball of mass 6kg moving with a velocity of 10ms-1 collides with a 2kg ball moving in the opposite direction with a velocity of 5ms-1. After the collision the two balls coalesce and move in the same direction. Calculate the velocity of the composite body

Answer 1

Answer:

The required velocity of the composite body is 25/4 ms⁻¹.

Explanation:

Let

• m₁ = 6 kg
• u₁ = 10 m/s
• m₂ = 2 kg
• u₂ = 5 m/s

and 'v' be the velocity of the composite body.

After the collision the two balls coalesce and move in the same direction.

By the law of conservation of momentum, the net momentum before the collision is equal to the net momentum after the collision.

Net momentum before collision :

= m₁u₁ + m₂u₂

= 6(10) + 2(-5)  [-ve since the ball is moving in the opposite direction]

= 60 - 10

= 50 kg m/s

Net momentum after collision :

= (m₁ + m₂)v

= (6 + 2)v

= 8v

Net momentum before collision = net momentum after collision

50 = 8v

 v = 50/8

 v = 25/4 ms⁻¹

Therefore, the velocity of the composite body is 25/4 ms⁻¹ moving in the direction of 6 kg ball.