Q.

Two spheres  P and Q  of 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  σ2 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 V→P and  Q alone in  L1 has terminal velocity  V→Q, then

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a

V→PV→Q=η1η2

b

V→PV→Q=η2η1

c

V→P.V→Q>0

d

V→P.V→Q<0

answer is A.

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Detailed Solution

For equilibrium of P : σ1Vg =ρ1Vg +TFor equilibrium of Q : σ2Vg +T=ρ2Vg Adding, σ1+σ2=ρ1+ρ2⇒σ2-ρ1=ρ2-σ1  Terminal velocity of P : VP=2r2g9η2σ2−ρ1→ Upward terminal velocity Terminal velocity of Q : VQ=2r2g9η1ρ2−σ1→ downword terminal velocity ratio=VPVQ=η1η2 And V→P  .V→Q   will be negative as they are opposite to each other
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Two spheres  P and Q  of 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  σ2 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 V→P and  Q alone in  L1 has terminal velocity  V→Q, then