A stone is tied to a string of length 2 m is whirled in a vertical circle with the other end of the string at the centre. At a certain instant of time, the stone is at its lowest position and has a speed 10 m/s. The magnitude of the change in its velocity as it reaches a position where the string is horizontal is
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Question

A stone is tied to a string of length 2 m is whirled in a vertical circle with the other end of the string at the centre. At a certain instant of time, the stone is at its lowest position and has a speed 10 m/s. The magnitude of the change in its velocity as it reaches a position where the string is horizontal is

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G1 Physics · Accepted Answer

From the bottom to the horizontal position the stone rises by 2 m, so v²=10²-2g(2)=60. The bottom and horizontal velocity directions are perpendicular, hence |Δv⃗|=√(10²+60)=√160 m/s. Hence D.