Everything Science Grade 12

CHAPTER 6. MOTIONIN TWO DIMENSIONS 6.4

This is an inelastic collision where momentum is conserved.

The momentum before= the momentum after.

The momentum after can be calculated by drawing a vector dia-

gram.

Step 2 : Calculate the momentum before the collision

p 1 (before) = m 1 vi 1 = (0,2)(3) = 0,6 kg· m·s−^1 east

p 2 (before) = m 2 vi 2 = (0,2)(4) = 0,8 kg· m·s−^1 south

Step 3 : Calculate the momentum after the collision.

Here we need to draw adiagram:

θ

0,6

0,8

p1+2(after)

p1+2(after) =

�

(0,8)^2 + (0,6)^2

= 1

Step 4 : Calculate the final velocity

First we have to find thedirection of the final momentum:

tan θ =

0 , 8

0 , 6

θ = 53, 13 ◦

Now we have to find themagnitude of the final velocity:

p1+2 = m1+2vf

1 = (0,2 + 0,2)vf

vf = 2,5 m· s−^153 , 13 ◦South of East

Exercise 6 - 3

1. A truck of mass 4500 kg travelling at 20 m·s−^1 hits a car from behind.The car
   (mass 1000 kg) was travelling at 15 m·s−^1. The two vehicles, now connected
   carry on moving in the same direction.