Homework Help: physics

Posted by paro on Monday, April 5, 2010 at 1:21pm.

Many cultures around the world still use a simple weapon called a blowgun, a tube with a dart that fits tightly inside. A sharp breath into the end of the tube launches the dart. When exhaling forcefully, a healthy person can supply air at a gauge pressure of 6.0 kPa.
What force does this pressure exert on a dart in a 1.4-cm-diameter tube?

physics - drwls, Monday, April 5, 2010 at 3:47pm
Multiply the gauge pressure in Pascals (6000) by the tube's circular inner area cross section in square meters (pi D^2/4) to get the force in Newtons.

pi D^2/4 = 1.54*10-4 m^2

I get about 1 Newton, which is about 1/4 pound force.
physics - gangadhar, Thursday, November 3, 2011 at 3:02am
Use the equation Pressure = Force / Area. Solve the equation for Force to get Force = Pressure * Area. Now, just plug in the values. Force = 0.006 Pa * (pi)0.008^2. Notice you need to divide the radius (0.008 m), not the diameter, in the equation for the area of a circle. The answer is 1.21 N.

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