Question

An object of mass 1 kg travelling in a straight line with a velocity of 10 ms~’ 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 velocity of the combined object.

Answer 1

(1) We are given that

Mass of object (m₁) = 1 kg

Velocity of object before collision (U₁) = 10 m/s

Mass of wooden block (m₂) = 5 kg

Velocity of object after collision (u₂) = 0 m/s

.’. Total momentum before the impact = m₁u₁ + m₂u₂

= 1 x 10 + 5 x 0 = 10 kg m/s

According to the law of conservation of momentum (When no external force act on the system)

Total momentum after the impact = 10 kg m/s

(2) Mass of the combined object,

M = Mass of object + mass of block = 1 + 5 = 6 kg

Let V be the velocity of the combined object after the impact.

Movement of combined objects

= Total momentum after the impact

i.e. 6 V = 10

V = 10/6 = 1.67 m/s