Question

Two objects, each of mass 1.5 kg are moving in the same straight line but in opposite directions. The velocity of each object is 2.5 ms-1 before the collision during which they stick together. What will be the velocity of the combined object after collision?

  • force and laws of motion CBSE Class 9
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Answer

Mass of one of the objects, m1 = 1.5 kg

Mass of the other object, m2 = 1.5 kg

Velocity of m1 before collision, v1 = 2.5 m/s

Velocity of m2, moving in opposite direction before collision, v2 = -2.5 m/s

(Negative sign arises because mass m2 is moving in an opposite direction)

After collision, the two objects stick together.

Total mass of the combined object = m1 + m2

Velocity of the combined object = v

According to the law of conservation of momentum:

Total momentum before collision = Total momentum after collision

m1v1 + m2v2 = (m1 + m2) v

1.5(2.5) + 1.5 (-2.5) = (1.5 + 1.5) v

3.75 – 3.75 = 3 v

v = 0

Hence, the velocity of the combined object after collision is 0 m/s.

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