A pumping machine pumps a liquid at a rate of 60 cc per minute at a pressure of 1.5 atmosphere. The power of the machine is

(A) 9 watts

(B) 6 watts

(C ) 9 kW

(D) None of these

Solution : Power = F.v , where F = force imparted by the machine , v = velocity of the liquid

P = p.A.v, Where p = pressure & A = effective area

= p dV/dt

= (1.5×10^{5} N/m^{2})(60 ×10^{-6} N/m^{2})

( 1 atm ≈ 10^{5} N/m^{2} )

= 9 watts