For rolling without slipping on an inclined plane, we can write Rmg‌sin‌θ=(mK2+mR2)α ⇒‌‌Rmg‌sin‌θ=m(K2+R2)α ⇒‌‌α=‌
Rg‌sin‌θ
K2+R2
⇒‌
α
R
=‌
g‌sin‌θ
1+‌
K2
R2
⇒‌‌a=‌
g‌sin‌θ
1+‌
K2
R2
  [∵a=‌
α
R
]... (i) Time period, t=√‌
2s
a
...(ii) From Eqs. (i) and (ii), we get t=√‌
2s
g‌sin‌θ
(1+‌
k2
R2
) For least time acceleration a should be maximum and K should be minimum and we know that K is least for solid sphere. So, time will be least for sphere. It means the body which will reach first at the bottom of the inclined plane is 4 , i.e. solid sphere.