Question

2 balls have masses of 50 gm and 100gm and they are moving along same line in same direction with velocity of 3m/s and 1.5m/s

Answer 1

so, do you want the momentum of the bodies?
if so, momentum =mass *velocity.
mass a =50 gram =50/1000 =0.05 kg.
mass b =100gram=100/1000=0.1 kg
the momentum of the first ball= 0.05*3= 0.15 kg m/s
 the momentum of the second ball= 0.1*1.5=0.1kg m/s

Answer 2

Question

2 Balls have have masses of 50 gm and 100 gm respectively and they as moving along the same line in the same direction with velocities of 3m/s and 1.5m/s respectively. They collide with eachother and after the collision, the first ball moves with a velocity of 2.5m/s. Calculate the velocity of the other ball after collision.

Given

$\implies \sf \: the \: mass \: of \: first \: ball \: = m_{1} \: = 50g \: = 0.05kg$

$\implies \sf \: mass \: of \: the \: second \: ball \: = m_{2} = 100g \: = 0.1kg$

$\implies \sf \: initial \: velocity \: of \: the \: first \: ball = u_{1} = 3m/s$

$\implies \sf \: initial \: velocity \: of \: the \: second \: ball \: = u_{2} = 1.5m/s$

$\implies \sf \: final \: velocity \: of \: the \: first \: ball \: = v_{1} = 2.5m/s$

Required to Find

$\implies \sf \: final \: velocity \: of \: the \: second \: ball \: = v_{2} = \: \: ?$

Solution

According to the law of conservation of momentum, total initial momentum = total final momentum.

$\sf \: m_{1} \: u_{1} + \: m_{2} \: u_{2} \: = m_{1} \: v_{1} + \: m_{2} \: v_{2}$

$\sf \: (0.05 \times 3) + (0.1 \times 1.5) = (0.05 \times 2.5) + (0.1 \times v_{2})$

$\sf \: 0.3 = 0.125 + 0.1 v_{2}$

$\sf \: 0.1 v_{2} \: = \: 0.3 \: - \: 0.125$

$\sf \: v_{2} \: = \: \dfrac{0.175}{0.1} = 1.75 \: m/s$

Remember !

• When no external force acts on two interacting objects, their total momentum remains constant. It does not change.

• When two objects collide, the total momentum before collision is equal to the total momentum after collision.