Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Homework Help: Determine angle for gun to be shot at

  1. Dec 2, 2008 #1


    User Avatar

    1. The problem statement, all variables and given/known data
    A toy gun fires marbles with a velocity v = 7m/s

    a) to hit a toy soldier that is 1.8 m away and 1.1 m higher than the gun, at what angle should the gun be aimed?

    b) Now assume that the toy soldier is dropped ( starting from rest) the instant the gun is fired. If the gun is aimed at the toy soldier when it is fired, at what height above the ground will the soldier be when it is hit by the bullet?

    2. Relevant equations

    a) Vx = 7cosx
    Vy = 7sinx

    1.8 = 7cosxt ...so.... t = 1.8/(7cosx) (x component)
    1.1 =7sinxt -4.9t^2 ( y component)

    3. The attempt at a solution

    a) wouldn't you just plug t into equation two and solve? thats what i did but im getting
    1.1cos^2x - 1.8 *cosx * sinx = -0.324

    how do i solve for x if i am only permitted to use a regular calculator?

    b) wouldn't b) be the same process but you would need to solve for the time at which they would hit?
  2. jcsd
  3. Dec 3, 2008 #2


    User Avatar
    Homework Helper

    1.1cos^2x - 1.8 *cosx * sinx = -0.324
    You can rewright the above equation as:

    1.1 = 1.8*tanx - 0.324*sec^2x
    1.1 = 1.8*tanx - 0.324*(1+tan^2x)
    Now solve for tanx by using quadratic equation formula
  4. Dec 3, 2008 #3


    User Avatar

Share this great discussion with others via Reddit, Google+, Twitter, or Facebook