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Homework Help: Projectile Motion problem help please

  1. Oct 24, 2012 #1
    1. The problem statement, all variables and given/known data

    Use 4 decimal places at each step to ensure accuracy.
    a) A rocket is launched vertically and remains in the air for 5.10 seconds until it hits the ground. Calculate the initial velocity of the rocket. Calculate the maximum height of the rocket (positive).
    vo = 24.99

    m/s (Note: You will need this initial velocity for parts b, c, and d)
    y = 31.8622


    b) The rocket is now launched with the same initial velocity as calculated in part A at an angle of 45 degrees. Calculate the time the rocket will be in the air for. Calculate the maximum height that the rocket will reach. Calculate the horizontal distance that the rocket will travel until it hits the ground.
    t = s

    y = m
    x = m

    2. Relevant equations
    idk sorry :(

    3. The attempt at a solution

    ok so i tried to do
    t = (v - vo) / -9.8

    and its wrong because i got
  2. jcsd
  3. Oct 24, 2012 #2
    If you don't know the kinematic equations, you won't be able to do solve these questions unless you know how to derive them yourself. You can find some of the formulas (not all of them, but you can derive the rest from the basic ones) in the sticky for this forum: https://www.physicsforums.com/showthread.php?t=110015
  4. Oct 24, 2012 #3
    Do you have a physics text book? If yes which one is it? I think I got through intro physics by studying the worked examples in my physics book (and also reading the book).
  5. Oct 25, 2012 #4
    This: t = (v - vo) / -9.8
    gives you only half of the time because its speed is (momentarily) zero at the top.
    Its speed is not zero when it hits the ground!
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