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April 1, 2015

April 1, 2015

Posted by **Devin** on Tuesday, December 5, 2006 at 9:19pm.

*=hole

()____________*___()

2. you're indoors, with a door 1m wide and 2.5m high. the wind blows past the door at 1 m /s. what is the net force on the door and its direction? the density of air is 1.2kh/m^3.

You look at a faucent and notice that the strema narrows as it falls. Suppose that the initial water speed is v1 and the initial area of the water faucent opening is A1. Findd the area of the water stream when it has fallen a distance H. The density of water is 1kg/liter and 1 liter is a volume of a cuber w. sides 0.1m.

4- a balooon filled w. helium (density 0.1785 g/L) see previous question for desnity of air and what a liter is). Assuming a baloon of radius 10cm and ignoring the mass of the baloon how much weight could the baloon lift?

You would get faster responses if you posted questions one at a time, and showed some of your work.

(1) Since the pipe is blocked at the end and the hole is 1/10 the pipe diameter, the velocity of the water leaving the hole must be 100 times a m/s, or 100 m/s. That seems very high to me. Get the height H by setting the kinetic energy leaving the hole equal to the potential energy increase at height H:

V = sqrt (2 g H)

Use the bernoulli equation to get the pressure differential bwtween the two sides of the door. The pressure will be lower on the outside where the wind is blowing by. The pressure difference is

(1/2) (density) V^2.

Multiply that by the door area for the force, which will be outward

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