For all parts of this problem, assume the effects of viscosity are negligible. (

Question

For all parts of this problem, assume the effects of viscosity are negligible.

(A) A fire-extinguishing system in a vehicle consists of a flat horizontal tank full of a liquid fluorocarbon under high pressure (20 atm gauge pressure). The tank is connected to anozzle held closed by a plug of metal that melts at a modest temperature. In the instant the metal melts, at what velocity does the liquid escape through the nozzle? Assume the fluorocarbon has a density of 1150 kg m3 and is incompressible, and that the external pressure is 1 atm.   

(B) A water cannon launch bursts of water 35 meters vertically into the air. Before the cannon nozzle opens, the water inside is stationary. What pressure is the water under at the instant the launch begins?

Explanation / Answer

A). From Bernauli's equation :

P1/rho* g + v12/2g + z1 = P2/rho* g + v22/2g + z2

as we know that z1 = z2

20 x 1.01 x 105 / (1150*9.8) + 0 + z1 = 1.01 x 105 / (1150*9.8) + v22/2g + z1

hence v22/2g = 19 x 1.01 x 105 / (1150*9.8)

v22 = 19 x 1.01 x 105 / (1150*9.8) * 2*9.8

v22 = 3337.391

v2 = 57.77 m/sec ..............Ans.

(B) P = rho*g*h

P = 1000*9.8*35 = 3.43 x 105 Pa Ans.

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