Question

Two plastic spheres of masses 10 g and 20 g are moving in a straight line in the same direction with velocities of 3 ms^–1 and 2 ms^–1 respectively. They collide with each other and after collision the plastic sphere of mass 10 g moves with a velocity of 2.5 ms^–1. Find the velocity of the second ball after collision.

• A. 2.5 ms^-1
• B. 2.25 ms^-1
• C. 3.0 ms^-1
• D. 4.0 ms^-1

Answer 1

The correct option is B

2.25 ms^-1

<p>given m₁ = 10 g = 0.01 kg, u₁ = 3 m/s, v₁ = 2.5 m/s, m₂ = 20 g = 0.02 kg, u₂ = 2&nbsp;m/s, v₂ = ?</p>

<p>total momentum before collision = m₁u₁+m₂u₂ = 3 x 0.01 + 2 x 0.02 = 0.07 kgm/s</p>

<p>total momentum after collision = m₁v₁ + m₂v₂ = 0.01 x 2.5 + 0.02 x v₂</p>

<p>according to the law of conservation of momentum</p>

<p>0.07 = 0.025 + 0.02 x v₂</p>

<p>v₂ = $\frac{0.07-0.025}{0.02}$</p>

<p>v₂ = 2.25 m/s</p>