A small sphere of radius r falls from rest in a viscous liquid. As a result, heat is produced due to viscous force. The rate of production of heat when the sphere attains its terminal velocity, is proportional to
A
r3
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B
r2
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C
r5
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D
r4
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Solution
The correct option is Cr5 Rate of heat produced dQdt=Fv×VT(∵VT=2r29η(ρ−σ)g)=6πηrVT×VT(∵VT∝r2)dQdt∝rVT2(∵VT∝r2)∴dQdt∝r5