Rotational MotionMedium
Question
A small mass attached to a string rotates on a frictionless table top as shown. If thetenstion in the string is increased by pulling the string causing the radius of the circularmotion to decreases by factor of 2, the kineticenergy of the mass will
Options
A.decrease by a factor of 2
B.remains constant
C.increase by a factor 2
D.increase by a factor 4
Solution
Accordingh to law of conservation of angular momentum
mv r = mv′ r′
vr = v′
v′ = 2v .......(i)
∴
or
[Using (i)]
K′ = 4K.
mv r = mv′ r′
vr = v′
v′ = 2v .......(i)
∴
or
[Using (i)]K′ = 4K.
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