JEE Main Physics question
A body of mass 2 kg makes an elastic collision with another body at rest and continues to move in the original direction with one fourth of its original speed. The mass of the second body which collides with the first is
Answer: (B)
Solution
v₁ = [(m₁−m₂)/(m₁+m₂)]u₁ = u₁/4 (given) ⟹ (m₁−m₂)/(m₁+m₂) = 1/4. With m₁ = 2 kg: 4(2−m₂) = 2+m₂ ⟹ 8−4m₂ = 2+m₂ ⟹ 6 = 5m₂ ⟹ m₂ = 1.2 kg.