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Find initial Velocity with only distance, angle, and acceleration.

  1. Oct 9, 2009 #1
    1. The problem statement, all variables and given/known data
    A cannon sends a projectile towards a target
    a distance 1580 m away. The initial velocity
    makes an angle 24◦ with the horizontal. The
    target is hit.
    The acceleration of gravity is 9.8 m/s2 .
    What is the magnitude of the initial veloc-
    ity?
    Answer in units of m/s.

    How high is the highest point of the trajec-
    tory?
    Answer in units of m.

    How long does it take for the projectile to
    reach the target? (Assume no friction)
    Answer in units of s.


    2. Relevant equations



    3. The attempt at a solution
     
  2. jcsd
  3. Oct 9, 2009 #2

    rl.bhat

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    Collect the relevant equations for projectile motion from any source.
     
  4. Oct 9, 2009 #3
    Ive spent about 2 hours trying and trying this problem but i can't figure out the answers.
    The equations i used were
    Vox=VoCos0o
    Voy=VoSin0o
    V^2=Vo^ plus 2a(x-xo)
    V=Vo plus at
     
  5. Oct 9, 2009 #4

    rl.bhat

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    Since there is no acceleration in the x direction, vox remains constant.
    Using the last equation you can find the time to reach the maximum height. Here V = 0, Voy = Vosinθ and a = g.
    Double that time is the time of flight t.
    Range of the projectile R = Vo*cosθ* t
     
  6. Oct 9, 2009 #5
    Vo is not given
     
  7. Oct 9, 2009 #6

    rl.bhat

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    First of all find t in terms of Vo, sinθ and g. substitute this value in the expression for R and solve for Vo.
     
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