1)

 Two spheres P and Q   for equal radii have densities  ρ1 and ρ2, respectively, The spheres are connected by a massless string and placed in liquids L1 and L2 of densities  σ1   and σ 2  and viscosities η1 and η2, respectively. They float in equilibrium with the sphere P  in L1  and sphere Q  in L2   and the string being taut (see figure). If  sphere  P alone in L2  has  terminal  velocity  vp  and Q alone in L1 has terminal velocity vQ, then

1032021544_p1.PNG

 


A) |VP||VQ|=η1η2

B) |VP||VQ|=η2η1

C) [V_{P}.V_{Q}>0

D) V_{P}.V_{Q}<0

Answer:

Option A,D

Explanation:

 For floating , net weight of system=  net upthrust.

  (ρ1+ρ2)Vg=(σ1+σ2)Vg

           Since string is taut,   ρ1<σ1     and  ρ2>σ2

                      vp=2r2g2η2(σ2ρ1)

                                                    (upward terminal velocity)

                          vQ=2r2g9η1(ρ2σ1)

                                                 ( downward  terminal velocity)

                      |vPvQ|=η1η2

   Further ,  ¯vP.¯vQ   will negative  as they are opposite  to each other.