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1)

A solid sphere of radius R makes a perfect rolling down on a plane which is inclined to the horizontal axis at an angle θ. If the radius  of gyration is k , then its  acceleration is 


A) gsinθ(1+k2R2)

B) gsinθ(R2+k2)

C) gsinθ2(R2+k2)

D) gsinθ2(1+k2R2)

Answer:

Option A

Explanation:

 By force balancing  perpendicular to the inclined plane

 N=mgcosθ

 By forces  balancing  parallel to inclined  plane,

mgsinθfr=mdvdt

  dvdt=mgsinθfrmv(t)=gsinθdt1mfr.dt

 Now, torque,    τ=Idωdt=r×Fr   and    I=mk2

      mk2dωdt=rFr    or   dωdt=rFrmk2

      ω(t)=Rmk2frdt

or    1mfrdt=k2Rω(t)=k2R2v(t)   (using ω=v/R)

       v(t)=gsinθdtk2R2v(t)

 or    v(t)=1(1+k2R2)gsinθdt

 So, acceleration, 

a(t)=dv(t)dt=gsinθ(1+k2R2)