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Homework Help: Velocity and acceleration of an army tank

  1. Jun 20, 2014 #1
    1. The problem statement, all variables and given/known data

    An army tank on a mountainside fires its gun horizontally. The shell strikes the ground at a horizontal distance of 6000 m away from the tank. As the vertical component of the shell’s striking velocity is vy=200 m/s, how soon after it is fired does the shell strike the ground? (g=10 m/s2)

    2. Relevant equations
    v^2=2ax (1)
    x=at^2/2 (2)
    3. The attempt at a solution
    then find t with (2) but why is it the component vy?
  2. jcsd
  3. Jun 20, 2014 #2


    User Avatar

    Staff: Mentor

    It isn't. If you use an equation involving vertical acceleration, then the other variables in the equation will be vertical displacement, vertical velocity, etc.

    Your mistake is that you mixed a vertical velocity and a horizontal distance in the one equation!
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