Laws of Motion

JEE Main level, single correct, medium

57 of 210

Question 57 of 210

An engine pumps water continuously through a hose. Water leaves the hose with velocity vv and mm is mass per unit length of the water jet. If this jet hits a surface and came to rest instantaneously, the force on the surface is

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Answer: (B) mv2m v^2

As power P=F.v.=Fℓt\mathrm{P}=F . v .=\frac{F \ell}{t}
 or, v(Mvt)=F.ℓt⇒Mv2=Fℓℓ⇒F=Mℓv2=mv2[∵Mℓ=m( given )]\begin{aligned} & \text { or, } v\left(M \frac{v}{t}\right)=\frac{F . \ell}{t} \\ & \Rightarrow \quad M v^2=F \ell \ell \\ & \Rightarrow \quad F=\frac{M}{\ell} v^2=m v^2 \\ & {\left[\because \frac{M}{\ell}=m(\text { given })\right]} \end{aligned}

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