A solid sphere is rolling down without slipping on an inclined plane of length 21 m with an acceleration of $5\,ms^{-2}$. The time taken by a circular disc to roll down without slipping to reach the bottom from the top of the same inclined plane is}
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For rolling bodies:
\[
a=\frac{g\sin\theta}{1+\frac{I}{mR^2}}
\]
Smaller moment of inertia gives larger acceleration.