Dynamics

Question 1

Two blocks block A and block B move towards each other and collide. Use Newton’s third law to explain why,during the collision, the change in momentum of block A is equal and opposite to the change in momentum of block B.

Answer 1

1. Force on A by B was equal AND opposite to force on B by A.
2. Force is rate of change of momentum and time of contact is the same

Question 2

Block A:
u1 = +0.4 ms-1
v1 = + 0.2 ms-1
Block B:
u2 = -0.25 ms-1
v2 = + 0.35 ms-1
Calculate, for the blocks, 1. the relative speed of approach,
2. the relative speed of separation.

Bonus ques: is the collision elastic or inelastic and why?

Answer 2

1. Speed of approach= u1 - u2= 0.4 + (-0.25)
   = 0.65
   2.
   v1 - v2 = -0.20 - -0.35 = 0.35 - 0.2= 0.15

Bonus: inelastic
Relative speed of seperation is not equal to or less than relative speed of approach