Physics Help Forum Finding time for velocity ( water hammer related)

 Thermodynamics and Fluid Mechanics Thermodynamics and Fluid Mechanics Physics Help Forum

 Mar 26th 2017, 09:23 AM #1 Junior Member   Join Date: Feb 2017 Posts: 4 Finding time for velocity ( water hammer related) Hello, The problem is given: I first found v0(final) from: $\displaystyle v0=sqrt(\frac {2*g*h}{lambda*\frac {l}{d}+1})$ $\displaystyle v0=sqrt(\frac {2*9.81*18}{0.03*\frac {400}{2}+1})$ v0 is 7.1 m/s 90% of v0 is v= 6.39 m/s. Time to reach v=6.39 m/s: $\displaystyle t=\frac {l*v0}{2*g*H}*log(\frac {v0+v}{v0-v})$ $\displaystyle t=\frac {400*7.1}{2*9.81*18}*log(\frac {7.1+6.39}{7.1-6.39})$ $\displaystyle t=10.28$ s But the answer key says it is 1 mins 20 secs Where may I go wrong? Thanks a lot