An object of mass 1 kg travelling in a straight line with a velocity of 10 ms–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.
Here,
Mass of the object, m1 = 1 kg
Velocity of the object, u1 = 10ms-1
Mass of the wooden block, m2 =5 kg
Velocity after collision, u2 =0 m/s
Let v be the velocity of the combined object after the collision
That is,
Total momentum just before the impact is,
m1u1 + m2u2 = 1 x 10 + 5 x 0 = 10 kg ms-1
Total momentum just after the impact is,
(m1 + m2) v = (1+5)v = 6v kg ms-1
Using the law of conservation of momentum,
6v = 10 
v = 10/6 = 5/3 = ms-1
Therefore,
Total momentum just after the impact= 6 x 5/3
= 10 ms-1.
