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Homework Help: Projectiles: Launch speed and horizontal distance

  1. Sep 14, 2011 #1
    New to the forums, just starting a physics 11 course online and having some troubles with formulas.

    1. The problem statement, all variables and given/known data

    Projectile shot straight upwards, flight time = 4.70 sec
    Second Launch at 45 degrees (horizontal range approx. 50-60 meters

    A) Find Launch Velocity
    B) Find Horizontal Range when shot at 45 degrees

    2. Relevant equations

    d = vit +1/2gt2

    V = - 1/2gt ("made" this one myself from above formula, unsure if correct)

    3. The attempt at a solution

    Launch velocity

    V = - 1/2gt
    g = -9.8m/s
    t = 4.7s

    V = -[((1/2(-9.8))(4.7)]
    V = -((-4.9)(4.7))
    V = 23.0 m/s

    I have no idea how to calculate the horizontal range, I need a formula that incorperates the 45 degrees

    Thanks in advance!
    1. The problem statement, all variables and given/known data

    2. Relevant equations

    3. The attempt at a solution
  2. jcsd
  3. Sep 14, 2011 #2


    User Avatar
    Homework Helper

    You can work from first principles: Calculate the vertical and horizontal components of the launch speed - using sin45 and cos 45 factors.
    The vertical component lets you calculate the flight time, the horizontal component with that time lets you calculate how far away it will land - the range.
    Many Physics texts will have a section where a formula is derived, so you can simply substitute the 23 m/s to get an answer [assuming 23 m/s is correct - it certainly is a reasonable answer]
  4. Sep 15, 2011 #3
    How would I do this? I am completly new to this and need a formula with a simple step-by-step guide on how to implement that formula to derive the answer.
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