Q.

STATEMENT-1: Two cylinders, one hollow (metal) and the other solid (wood) with the same mass and identical dimensions are simultaneously allowed to roll without slipping down an inclined plane from the same height. The hollow cylinder will reach the bottom of the inclined plane first.

STATEMENT-2: By the principle of conservation of energy, the total kinetic energies of both the cylinders are identical when they reach the bottom of the inclined plane.    [2008]

1 Statement-1 is True, Statement-2 is True; Statement-2 is a correct explanation for Statement-1  
2 Statement-1 is True, Statement-2 is True; Statement-2 is NOT a correct explanation for Statement-1  
3 Statement-1 is True, Statement-2 is False  
4 Statement-1 is False, Statement-2 is True  

Ans.

(4)

In case of pure rolling on inclined plane acceleration of a body

a=gsinθ1+IMR2

For hollow cylinder  IMR2=MR2MR2=1

For solid cylinder  IMR2=12MR2MR2=12

Hence acceleration of solid cylinder is more than hollow cylinder and therefore solid cylinder will reach the bottom of the inclined plane first.

In the case of rolling there will be no work done by friction. Therefore total mechanical energy remains conserved.

  (K.E)solid=(K.E)hollow=decrease in P.E=mgh