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Need Help Projectile Motion - Hitting Target with toy gun

  1. Nov 16, 2014 #1
    Hey, I need help with a lab I'm doing in class. The goal is to hit a target on the ground by shooting a bullet from a toy gun. Our distance from the target will be assigned to us by our teacher and I need to calculate the initial velocity of the gun and then hit the target by only changing the angle or the vertical displacement. How would I go about getting the initial velocity easily and calculating the angle or vertical displacement need to hit the target. Also what would be the best angle to use. Air resistance is ignored for this entire question. Thanks.

    Relevant Equations


    d = v1t + 0.5at^2

    My Attempt

    1. Get initial velocity and calculate horizontal and vertical speeds with an angle of 45
    2. Get time for horizontal component
    3. Use time in vertical component for vertical displacement
     
  2. jcsd
  3. Nov 17, 2014 #2

    PeterDonis

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    2016 Award

    Staff: Mentor

    Hi, BobGStop, and welcome to PF!

    Your "attempt" doesn't actually show any work. It lists the steps you would take to solve the problem, but doesn't actually describe any work you've done at accomplishing those steps. What work have you done?
     
  4. Nov 17, 2014 #3
    1. Got initial velocity of 7.57 m/s - I shot the gun horizontally and did displacement over time
    2. Used velocity to do 7.57cos45 and 7.57sin45 to get horizontal and vertical velocity of 5.35
    3. I set the horizontal displacement to 3 and sloved for a time of 0.42
    4. Used the the time to solve for a vertical displacement of 1.002

    When I tried to get my target using a angle of 45 and height of 1 m I overshot it by half a meter. I believe it's because my initial velocity is wrong but I am not sure.
     
  5. Nov 17, 2014 #4
    Edit - sorry wrote the wrong time and vertical displacement
    1. Got initial velocity of 7.57 m/s - I shot the gun horizontally and did displacement over time
    2. Used velocity to do 7.57cos45 and 7.57sin45 to get horizontal and vertical velocity of 5.35
    3. I set the horizontal displacement to 3 and sloved for a time of 0.56
    4. Used the the time to solve for a vertical displacement of 1.45
    When I tried to get my target using a angle of 45 and height of 1 m I overshot it by half a meter. I believe it's because my initial velocity is wrong but I am not sure.
     
  6. Nov 17, 2014 #5

    PeterDonis

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    2016 Award

    Staff: Mentor

    I assume this is because your teacher told you to use that distance from the target?

    What does this time represent? Is it the time you are really interested in?

    Can you give some more detail about this step?

    How does this compare with what the relevant equations would predict for an angle of 45 degrees and a vertical displacement of 1 meter?
     
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