A body of mass 20kg moving with a velocity of 80ms(^{-1}) collides with another body of mass 30kg moving with a velocity of 50ms(^{-1}). If they both moved in the same direction after collision, find their common velocity if they moved in the :
(a) same direction before collision ; (b) opposite direction before collision.
Explanation
(a)
Momentum before collision = ((20 times 80) + (30 times 50) = 1600 + 1500)
= (3100 kgm/s)
Momentum after collision = 50v kgm/s
Momentum before collision = Momentum after collision
(3100 = 50v)
(v = frac{3100}{50} = 62m/s)
(b)
Momentum before collision = ((20 times 80) – (30 times 50) = 1600 – 1500)
= (100 kgm/s)
Momentum after collision = (50v kgm/s)
(therefore 100 = 50v)
(v = 2m/s)