A  water jet, whose cross-sectional area 'a' strikes a wall making an angle \theta with the normal and rebounds elastically. The velocity of water of density 'd' is v. Force exerted on the wall is : 

  • Option 1)

    2av^{2}d\cos \theta

  • Option 2)

    2av^{2}d\sin \theta

  • Option 3)

    2avd\cos \theta

  • Option 4)

    2avd\sin \theta

 

Answers (1)

As we discussed in concept

Impulse Momentum Theorem -

\vec{F}=\frac{d\vec{p}}{dt}

\int_{t_{1}}^{t_{2}}\vec{F}dt=\int_{p_{1}}^{p_{2}}\vec{dp}

- wherein

If \bigtriangleup t  is increased, average force is decreased

 

 Change in momentum

\vec{\Delta p}\:=\:mvcos\theta -(-mvcos\theta)

        = -2mvcos\theta

        = 2(Volume\times\:density)\:vcos\theta

        = 2(av\rho )vcos\theta\:=\:2av^{2}\rho cos\theta


Option 1)

2av^{2}d\cos \theta

Option 2)

2av^{2}d\sin \theta

Option 3)

2avd\cos \theta

Option 4)

2avd\sin \theta

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