Page No 127: - Chapter 9 - Force & Laws Of Motion - Ncert Solutions class 9 - Science
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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 = 0.1 kg
Mass of the other object, m2 = 200 g = 0.2 kg
Velocity of m1 before collision, 
m/s
Velocity of m2 before collision, 
m/s
Velocity of m1 after collision, 
Velocity of m2 after collision = 
According to the law of conservation of momentum:
Total momentum before collision = Total momentum after collision
Hence, the velocity of the second object becomes 1.165 m/s after the collision.
