A man running with a uniform speed ‘u’ on a straight road observes a stationary bus at a distance ‘d’ ahead of him. At that instant, the bus starts with an acceleration ‘a’. The condition that he would be able to catch the bus is
A
d≤u2a
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B
d≤u22a
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C
d≤u23a
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D
d≤u24a
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Solution
The correct option is Bd≤u22a Let the man meet the bus at time t. Velocity of the man be u, acceleration of the bus be a, then ut=12at2+d For the time to be positive, the discriminant of the above expression should be greater than or equal to zero. Required condition d≤u22a