1.

An annular disc of radius `r_(1 )= 10 cm` and `r_(2) = 5 cm` is placed on a water surface. Find the surface tension force on the disc if we want to pull it from water surface. Take coefficient of surface tension as `sigma= 7 xx10^(-3) N//m, g = 10 ms^(-2)`. A. `6782.4dune`B. `67.82dyne`C. `678.24dyne`D. none of these

Answer» Correct Answer - A
`F=2pir_1T+F=2pir_2T`
`=(2pi(r_1+r_2)T`
`=2xx3.14(10+5)(72)=6782.4` dyne


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