NCERT Solutions for Class 9 Science Chapter 9
Force and Laws of Motion
NCERT Books for Session 2022-2023
CBSE Board and UP Board
Exercises Questions
Page No-129
Questions No-15
An object of mass 1 kg travelling in a straight line with a velocity of 10 m s–1 collides with, and sticks to, a stationary wooden block of mass 5 kg. Then they both move off together in the same straight line. Calculate the total momentum just before the impact and just after the impact. Also, calculate the velocity of the combined object.
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Mass of the object, m1 = 1 kg
Velocity of the object before collision, v₁ = 10 m/s
Mass of the stationary wooden block, m₂ = 5 kg
Velocity of the wooden block before collision, v₂= 0 m/s
∴ Total momentum before collision = m₁ v₁ + m₂ v₂
= 1 (10) + 5 (0) = 10 kg m s ⁻¹
It is given that after collision, the object and the wooden block stick together.
Total mass of the combined system = m₁ + m₂
Velocity of the combined object = v
According to the law of conservation of momentum:
Total momentum before collision = Total momentum after collision
m₁ v₁ + m₂ v₂ = (m1+ m₂) v
1 (10) + 5 (0) = (1 + 5) v
V=10/6 = 5/3 m/s
The total momentum after collision = 10 and velocity of combined object is 5/3
m/s.
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