Question

# Initially car A is 21 m ahead of car B. Both start moving at time t=0 in same direction along straight line. if A is moving with constant velocity 20 m/s and B starts from rest with an acceleration 2m/s2 towards A, then the time when car B will catch the car A is

A
21s
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B
22s
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C
10s
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D
Can never catch A
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Solution

## The correct option is A 21sThe relative speed of B wrt A will be VBA=VB−VA=20−0=−20m/stheir relative acceleration will be aBA=aB−aA=2−0=2m/s2the distance traveled will be given by s=ut+12at2=−20t+122×(t)2=21meteron solving it we get t=21secJust employ the Shridharacharya Formula t=−b±√b2−4ac2aWhere t is root of at2+bt+c=0

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