You are on a fire team in Iraq. You are manning a piece of artillery that fires

Question

You are on a fire team in Iraq. You are manning a piece of artillery that fires a 15kg projectile out of a 12m cannon with a constant in barrel force of 1500N. The coefficient of friction is .22 between shell and barrel, the barrel is at a fixed tilt of 30 degrees, and the wind is currently blowing directly South with 15N of effective force. An enemy vehicle is detected coming straight at your position from the North. It is maintaining a constant velocity of 40 m/s and is currently 1000m away. When do you open fire?

Explanation / Answer

frictional force =mg cos(30) = 28N

so Net force = 1500-28 = 1472N

energy consrevation 0.5mv2 = 1472*12

v=48.53m/s

time of flight = 2*(48.53*sin(30)/9.8) =4.952sec

so d = 48.53cos(30)*4.952 - 0.5*1*4.9522

= 208.127-12.26

= 195.86m

so time after which fire will start = (1000-195.86)/40 =20.10sec

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