Momentum and Collisions

 

 

1.       A truck of mass 2kg travels at 8 m/s towards a stationary truck of mass 6kg. After the collision they stuck together and move off in the same direction. What is their common velocity?

a.       16kgms^-1 = (2+6 kg)v so 8v = 16 and v =2 ms^-1

2.       A car of mass 2000kg, traveling at 10m/s, has a head on collision with a small sports car of mass 500kg. If both cars stop dead on colliding, what was the velocity of the sports car before the collision? Momentum after = 0 so (2000 x 10) + (500 x v) so 500v = 20000 and v = 40 ms^-1

3.       A man wearing a bullet proof vest stands on roller skates. His total mass is 80kg. A bullet of mass 20g is fired at him at a speed of 400 m/s. If the bullet is stopped by the vest and falls to the ground, what velocity will the man move at? Momentum before = (0.02kg x 400) + 0 = 8k ms^-1

a.       Momentum after = 0 + (80kg x v) = 8 kg ms^-1  so 80v = 8 so v = 0.1 ms^-1 after being hit

How does your answer compare with “the movies”? They aren’t real. (but then you knew that)