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XyziceyX Male
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  #1 Old 10-07-2012 Default physic

a jet of water hits wall normally with a speed v.the pressure on the wall is p.if the speed of the jet of water is 4v ,what is the pressure on the wall? Answer is 16p.but I dunno how to prove it.anyone help to prove this.thanks
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frankchong
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  #2 Old 10-07-2012 Default Re: physic

1. Force = rate of change of momentum
2. Mass of water delivered per unit time is proportional to velocity
3. Momentum of water delivered per unit time = mass*velocity
4. Substitute 2 in 3 you get momentum of water delivered per unit time is proportional to square of the velocity, which from 1, says it is proportional to the force/pressure

So, we have pressure P proportional to V^2, substituting 4V for V you get 16V.
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XyziceyX Male
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  #3 Old 10-07-2012 Default Re: physic

why the mass of water delivered per unit time is proportional to velocity?which formula?
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