Question

A wagon weighing 1000 kg is moving with a velocity 50 km h^–1 on smooth horizontal rails. A mass of 250 kg is dropped into it. The velocity with which it moves now is 

(A) 2.5 km h^–1 

(B) 20 km h^–1 

(C) 40 km h^–1 

(D) 50 km h^–1

Answer 1

Correct option: (C) 40 km h^–1

Explanation:

m₁ = 1000 kg

v₁ = 50 kmph

m₂ = 1000 + 250 = 1250 kg.

v₂ = 2

by principle of conservation of momentum,

m₁v₁ = m₂ v₂ 

v₂ = {(m₁v₁) / (m₂)}

= {(1000 × 50) / (1250)}

v₂ = 40 kmph