A train is running at a speed of 72km/hr. A boy runs inside the train in same direction (as that of train) with a speed of 10km/hr with respect to the train. Find the velocity of boy as seen from the ground.
A
62km/hr along the direction of motion of train
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B
72km/hr opposite to direction of motion of train
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C
82km/hr along the direction of motion of train
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D
None of these
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Solution
The correct option is C82km/hr along the direction of motion of train Let +vex axis along the direction of motion of train. ⇒velocity of train w.r.t ground →vt,g=72^ikm/hr
Velocity of boy w.r.t. train, →vb,t=10^ikm/hr
Velocity of boy w.r.t ground: ⇒→vb,g=→vb,t+→vt,g
Or, →vb,g=(10^i+72^i)km/hr ∴→vb,g=82^ikm/hr
Hence, velocity of boy w.r.t ground is 82km/hr along the direction of motion of train.