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Old Sep 21st 2011, 02:02 PM   #1
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Finding the angle for a bullet to hit a target

Hi, I'm having trouble with a particular homework problem.

A rifle has muzzle velocity 450 m/s.
If you're 53.0 m from a target the same height as the rifle, at what angle above the horizontal should you aim in order to hit the target?

I tried using the equation one of the tutors gave me which was x = Velocity *sin 2(theta)/g, but it gave me a number less than 1.

All help is appreciated
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Old Sep 21st 2011, 02:29 PM   #2
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Check your units - the equation you gave has units of time, not distance. The correct equation is D = V^2/g sin(2 theta).

Here's where it comes fromn: the time it takes for the bullet to rise and then fall back to its original height isT= (2V/g)sin(theta). And the horizontal distance it travels in time t is D= VTcos(theta). So you can combine these two equations to get D = (2V^2/g)sin(theta)cos(theta). Finally, apply the trig identity sin(2 theta) = 2 sin(theta)cos(theta) to get D = V^2/g sin(2 theta). Now yuo can solve for theta.

Last edited by ChipB; Sep 21st 2011 at 02:33 PM.
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Old Sep 21st 2011, 02:32 PM   #3
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I retract that statement, lol

Last edited by tud10327; Sep 21st 2011 at 02:37 PM.
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Old Sep 21st 2011, 02:53 PM   #4
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Nvm, thank you so much for the help

Last edited by tud10327; Sep 21st 2011 at 03:08 PM.
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