Question

The freight cars a and b have a mass of 20 mg and 15 mg, respectively. determine the velocity of a after collision if the cars collide and rebound, such that b moves to the right with a speed of 2 m>s. if a and b are in contact for 0.5 s, find the average impulsive force which acts between them.

Answer 1

mass of freight car A = 20Mg = 20,000 kg
mass of freight car B = 15Mg = 15,000 kg
initial velocity of freight car A = -3m/s
initial velocity of freight car B = 1.5 m/s
final velocity of freight car B = - 2m/s [ assuming right direction is negative and left direction is positive ]

now, from conservation of linear momentum,
20,000 × -3 + 15,000 × 1.5 = 20,000 × v + 15,000 × -2

v = -0.375 m/s [ right direction]

now, Force × time, = change in momentum
= (20,000 × 3 - 20,000 × 0.375)
= 52,500 Ns

so, F × 0.5 = 52,500

F = 105000N or , 105kN

hence, force = 105kN