Question

Two particles A and B of masses 20 g and 30 g respectively are at rest at a certain time. Because
of the forces exerted by them on each other, the particles start moving. At a given instant, particle
A is found to move towards east with a velocity of 6 cm/sec. What is the velocity of particle B at
this instant (in cm/s)?​

Answer 1

Solution :-

• Mass of A = 20 g

• Mass of B = 30 g

Initially both the particles are at rest

Hence , the initial momentum of the system ( mass A + mass B ) is zero

➽ Pi = 0

Now ,

• Mass of A = 20 g

• Velocity of A = 6 cm /s

• Mass of B = 30 g

As no external force is acting on the system the total momentum of the system is conserved

By applying law of conservation of momentum ,

➽ Pi = Pf

➽ 0 = ma x v a + mb x v b

➽ - mb x vb = ma x va

➽ vb = - ma x va / mb

➽ vb = - 20 x 6 / 30

➽ vb = - 120 /30

➽ vb = -4 cm /s

The velocity of the particle is 4 cm /s towards the west