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Water jet coming out of a stationary horizontal tube at speed v strikes horizontally a massive wall moving in opposite direction with same speed. Water comes to rest relative to wall after striking. Treating A as cross-section of jet and density of water as `rho` Select the correct alternative(s)A. force exerted on the wall is `2rhoAv^(2)`B. force exerted on the wall is `4rhoAv^(2)`C. rate of change of kinetic energy of water jet striking the wall is `8rhoAv^(3)`D. rate of change of kinetic energy of water jet striking the wall is zero. |
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Answer» Correct Answer - B::D mass rate of strike `(dm)/(dt) = A(2v)rho` Change in velocity during strike `=Deltav=vec(v)_(f)-vec(v)_(i)=(-v)-(v)=-2v` Thrust force on jet `=Deltav (dm)/(dt)=(dm)/(dt)(-2v)=-4rhoAv^(2)` Thrust force on wall =-Thrust force on jet `=4rhoAv^(2)` `(d(KE))/(dt)=1/2 (dm)/(dt) (v_(f)^(2))-1/2(dm)/(dt)(v_(i)^(2))=1/2(dm)/(dt)[(-v)^(2)-v^(2)]=0` |
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