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Question

A train is running at a speed of 72 km/hr. A boy runs inside the train in same direction (as that of train) with a speed of 10 km/hr with respect to the train. Find the velocity of boy as seen from the ground.

A
62 km/hr along the direction of motion of train
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B
72 km/hr opposite to direction of motion of train
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C
82 km/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 C 82 km/hr along the direction of motion of train
Let +ve x axis along the direction of motion of train.
velocity of train w.r.t ground vt,g=72^i km/hr
Velocity of boy w.r.t. train,
vb,t=10^i km/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^i km/hr
Hence, velocity of boy w.r.t ground is 82 km/hr along the direction of motion of train.

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