Class 9 Science Force and Laws of Motion: NCERT Solutions for Question 11
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 m s-1 before the collision during which they stick together. What will be the velocity of the combined object after collision?
Mass of first objects, m1 = 1.5 kg
Mass of second 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)
We know that
Total momentum before collision = Total momentum after collision
m1v1 + m2 v2 = (m1 + m2) v
1.5(2.5) + 1.5 (−2.5) = (1.5 + 1.5) v
3.75 − 3.75 = 3 v
v = 0 / 3 = 0
Hence, the velocity of the combined object after collision is 0 m/s.
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