Q.

Two stones of masses m and 2m are whirled in horizontal circles, the heavier one in a radius r/2 and the lighter one in radius r. The tangential speed of lighter stone is n times that of the value of heavier stone when they experience same centripetal forces. The value of n is           [2015]

1 4  
2 1  
3 2  
4 3  

Ans.

(3)

Let v be tangential speed of heavier stone. Then, centripetal force experienced by lighter stone is

          (Fc)lighter=m(nv)2r

and that of heavier stone is (Fc)heavier=2mv2(r/2)

But (Fc)lighter=(Fc)heavier                              (given)

  m(nv)2r=2mv2(r/2) or, n2(mv2r)=4(mv2r)

        n2=4 or n=2