Theory question 108
DynamicsA body of mass 20 kg moving with a velocity of 80 ms−1 collides with another body of mass 30 kg moving with a velocity of 50 ms−1. If the two bodies moved together 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.
Show the model answer
Model answer
(a) 20(80) + 30(50) = 50v, so 3100 = 50v and v = 62 ms⁻¹.
(b) 20(80) − 30(50) = 50v, so 100 = 50v and v = 2 ms⁻¹ (in the 20 kg body's direction).
Explanation
Momentum is conserved; give opposite velocities opposite signs.