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Standard XII

Physics

Relative Velocity in 2D

Man A is sitt...

Question

Man A is sitting in a car moving with a speed of 54 km/hr observes a man B in front of the car crossing perpendicularly a road of width 15 m in three seconds. Then the velocity of man B (in m/s) will be

5 \sqrt{10}

towards the car at some angle

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5 \sqrt{10}

away from the car at some angle

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5 perpendicular to the road

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15 along the road

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Solution

The correct option is B $5 \sqrt{10}$ away from the car at some angle
Velocity of A $\Rightarrow 54 k m / h r \Rightarrow 15 m / s .$
Since the motion of B is seen in perpendicular direction by A.
$∴$ Its component of velocity will be 15 m/s in the direction of motion of A in same direction. Now Its velocity is 5 m/s in perpendicular direction .
$∴$ Magnitude of velocity $\Rightarrow \sqrt{5^{2} + 15^{2}} \Rightarrow \sqrt{250} \Rightarrow 5 \sqrt{10} m / s$ at some angle away from the car.

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