# Impossible Problem

1. Oct 19, 2005

### richbasterd21

I got this problem in physics today and i have no idea how to do it:

You are on a firing team in Iraq. You are manning a piece of artillery that fires a 15kg. projectile out of a 12mm barrel. with a constant in barrel force of 1500N. The mew(i think that is how you spell it) is .22. the barrel is tilted at 30 degrees and the wind is blowing directly at you at you with 15N of force. An enemy vehicle is coming directly at you at 40 m/s and is currently at 1000m away. When do you fire? I need help on finiding the acceleration, f applied in both x and y directions, normal force and all of the rest of the info!!

2. Oct 19, 2005

### pizzasky

Wow! A tough question indeed. Do you have to assume that the projectile is fired at ground level (i.e. the level where it eventually hits the enemy vehicle)?

When the projectile is travelling in the barrel, what is the net force acting on it? Observe that both the resultant force and acceleration are constant, so you can apply Newton's 2nd Law and some Kinematics equations in determining the speed of the projectile when it leaves the barrel and the time taken.

When the projectile is travelling in the air, resolve its speed into 2 perpendicular components. The wind affects only the horizontal component, and gravity affects only the vertical component. Use Newton's 2nd Law to determine the constant acceleration in both directions, and some Kinematics equations to calculate the horizontal distance it has covered when it hits the ground and the time taken to do so.

Finally, add the 2 periods of time above, and calculate the corresponding range of the projectile and solve the question!

3. Oct 19, 2005

### pizzasky

Hmmm...There's something odd about your question. Is the barrel only 12mm in length? Isn't this an unrealistic measurement?

Also, what is your value of g(acceleration due to gravity)? Did you use 9.8, 9.81 or 10 $$ms^{-2}$$?

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