Class 9 Science Force and Laws of Motion: NCERT Solutions for Question 4

This page offers a step-by-step solution to the specific question NCERT Class 9th Science - Force and Laws of Motion | two objects of masses 100 g and 200 g are moving a Answer from NCERT Class 9th Science, Chapter Force and Laws of Motion.
Question 4

Two objects of masses 100 g and 200 g are moving along the same line and direction with velocities of 2 m s-1 and 1 m s-1, respectively. They collide and after the collision, the first object moves at a velocity of 1.67 m s-1. Determine the velocity of the second object.

Answer

Mass of one of the objects, m1 = 100 g = 100/1000 = 0.1 kg 

Mass of the other object, m2 = 200 g = 200/1000 = 0.2 kg

Velocity of m1 before collision, v1 = 2 m/s

Velocity of m2 before collision, v2 = 1 m/s

Velocity of m1 after collision, v3 = 1.67 m/s

Velocity of m2 after collision = v4 = ?

By law of conservation of momentum :

Total momentum before collision = Total momentum after collision

 m1v1 + m2v2 = m1v3 + m2v4

(0.1)2 + (0.2)1 = (0.1)1.67 + (0.2)v4

0.4 = 0.167 + 0.2v4

 v4 = 1.165 m/s

The velocity of the second object after collision 1.165 m/s.

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