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Question

A solid sphere of radius R starts rotating on rough horizontal surface with translational velocity V0 and initial angular velocity ω0=2V03R . The sphere starts pure rolling after some time t. if V is the translational velocity at pure rolling. Assume uniformly accelerated motion up to start of pure rolling:
if S is the distance covered by the sphere in rotational motion up to the instant at which pure rolling starts, find the velocity (translational) of the sphere during the pure rolling

A
3338St
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B
3138St
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C
3833St
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D
3738St
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Solution

The correct option is C 3833St
Draw a diagram of given problem.

Find angular acceleration of the sphere.
Formula used:ω=ω0+αt
Given,
ω0=2V03R

V0=32Rω0
according to diagram, angular momentum is conserved about A,
L1=L2
Therefore,
25mR2ω0+mV0R=25mR2ω+mVR

25mR2×2V03R+mV0R=25mR2VR+mVR

V0=2119V(i)
Now, according to question ω and V are translational velocity for pure rolling starts,
ω=ω0+αt
From equation (i),we get
α=5V19Rt
Where, t is time when pure rolling starts.

Find angle by which sphere rotates.
Formula used:θ=ω0t+12αt2
Pure rolling starts when sphere start rotated by an angle θ,
Therefore,
θ=ω0t+12αt2

θ=2V03Rt+12.5V19Rt.t2

θ=3338VtR

Rθ=S=3338Vt
Therefore,
Translational velocity(V),
V=3833St

Final answer: (d)

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