A car is moving along a straight track with a velocity of 20 m/s due East. After 5 s it starts retracing its path with the uniform velocity $\overrightarrow{v}$. If its average velocity after 15 s is zero, then $\overrightarrow{v}$ is:

Given, a car moving in a straight track covered A to B towards the east with velocity, v₁=20 m/s

Time=t₁=5 s

Displacement = v₁t₁ = 100 m

It started retracing back and reached A in t = 10 s with velocity=v

So, after t = 15 s, total displacement =0

Therefore, avg. velocity =0

From B to A:

100m=v x 10 s

v=10 m/s towards the West