Question

A car travelling north at 20 m/s turns and then travels south at 20 m/s. The change in its velocity is 

1. Zero
2. 40 m/s north
3. 40 m/s south 
4. 20 m/s north

Answer 1

Correct Answer : 3. 40 m/s

Explanation :

Let north be represented by - i, thus south is represented by + i.

∴  initial velocity, V_i = - 20 i

and final velocity, V_i = 20 i

change in velocity , ΔV = V_i - V_i = 20 i - (-20 i)

= + 40 i

ΔV = 40 m/s south.