Everything Science Grade 12

6.4 CHAPTER 6. MOTIONIN TWO DIMENSIONS

But according to the question, marble 1 is moving after the colli-

sion, therefore marble 1moves to the right at 4 m·s−^1. Substitut-

ing this value for vf 1 into Equation 6.5, we can calculate:

vf 2 =

0 , 3 − 0 , 05 vf 1

0 , 1

=

0 , 3 − 0 , 05 × 4

0 , 1

= 1 m· s−^1

Therefore marble 2 moves to the right with a velocity of 1 m·s−^1.

Example 10: Colliding Billiard Balls

QUESTION

Two billiard balls eachwith a mass of 150 g collide head-on in an elastic col-

lision. Ball 1 was travelling at a speed of 2 m· s−^1 and ball 2 at a speed of

1 ,5 m· s−^1. After the collision, ball 1 travels away from ball 2 at a velocity of

1 ,5 m· s−^1.

1. Calculate the velocity of ball 2 after the collision.


2. Prove that the collision was elastic. Show calculations.

SOLUTION

Step 1 : Draw a rough sketch of the situation

1 2 1 2

Before Collision After Collision

1 ,5 m· s−^1?

2 m· s−^11 ,5 m· s−^1

Step 2 : Decide how to approach the problem

Since momentum is conserved in all kinds of collisions, we can

use conservation of momentum to solve for the velocity of ball 2

after the collision.

Step 3 : Solve problem