A jet of water from a fire hose impinges horizontally on a wall as indicated in

Question

A jet of water from a fire hose impinges horizontally on a wall as indicated in the figure. The speed of the water is u before it strikes the wall (see figure) and it is assumed that the water has no velocity component perpendicular to the wall after it has hit the wall. The cross section of the water jet is a. The density of the water is p. 1. Find the force F the water exerts on the wall. The magnitude of F should be expressed in terms of p, a, and u. 2. Numerical example: p = 1000 kg/m^3, a = 0.0025 m^2, u = 60 m/s. Now compute F. Compare the result with the force on a man, of mass 70 kg, in the gravitational field of the Earth. 3. How far will a water jet from a hose reach before its hits the ground, if it is directed horizontally 1 m above the ground and the muzzle velocity is u = 60 m/s? 4. A stream of water impinges on a block B as indicated on the sketch. At a certain time, the block has velocity v < u relative to the ground as shown. The velocity of the water before it strikes the block is u relative to the ground. The cross section of the jet is still a and the density p. Find the force that the water jet exerts on the block B.

Explanation / Answer

1) force = 0.5*p*a*v^2 2) F = 4500 N 3) V = u^2-sqrt(2gh) = 55.57 m/s

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