First slide
Relative velocity in 1-d
Question

A bird flies to and fro between two cars which move with velocities v1=20 m/s and v2=30 m/s. If the speed of the bird is v3=10 m/s and the initial distance of separation
between them is d=2 km, find the total distance covered by the bird till the cars meet.

Moderate
Solution

 Time to meet the cars: t=dv1+v2

Distance travelled by bird in this time

s=v3t=v3dv1+v2=10×2000(20+30)=400m

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