InterviewSolution
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InterviewSolution
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if a ball of steel (density `rho=7.8 g//cm^(3)`) attains a terminal velocity of `10 cm//s` when falling in a tank of water (coefficient of viscosity, `eta_(water) =8.5xx10^(-4)`Ps s), then its terminal velocity in glycerine `(rho =1.2 g//cm^(2), eta =13.2 Pa s)` would be nearlyA. `6.45xx10^(-4)cm//s`B. `1.5xx10^(-5)cm//s`C. `1.6xx10^(-5)cm//s`D. `6.25xx10^(-4)cm//s` |
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Answer» Correct Answer - D Here, `rho_(s)=7.8 g//c^(3), v_(1) =10 cm//s`, `eta_(water) =8.5xx10^(-4)Pa S` `rho_(w)=1, rho_(g) =1.2 g//cm^(3), eta_(g) =13.2 Pa S, v_(2)=?` As terminal velocity `v=(2r^(2)(rho-rho_(0))g)/(9eta)` `:. v prop((rho-rho_(0)))/(eta)` `(v_(2))/(v_(1))=((rho-rho_(g)))/(eta_(g))xx(eta_(water))/((rho-rho_(w)))` `=((7.8-1.2))/(13.2)xx(8.5xx10^(-4))/((7.8-1)) = (6.6xx8.5xx10^(-4))/(13.2xx6.8)` `(v_(2))/(v_(1)) =0.625xx10^(4)` or `v_(2) =0.625xx10^(-4) xxv_(1)` `v_(2)=0.625xx10^(-4)xx10= 6.25xx10^(-4) cm//s` |
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