A ball is thrown in the air @ 30m/s

  1. 1. The problem statement, all variables and given/known data
    A ball is thrown straight up with an initial speed of 30m/s,
    (a) Show that the time it takes to reach the top of its trajectory will be 3 seconds.
    (b) Show that it will reach a height of 45m (neglecting air resistance).

    2. Relevant equations
    Earth's gravity = 9.8 meter/second² (Professor said to just round it to 10).
    Equation unknown.
    d=1/2(g)t² ?

    3. The attempt at a solution
    (a) Played around with Subtracting negative -9.8m/s² (is it considered negative since the ball gets thrown up? - Instead of it coming down?).

    (b) 45m = 1/2(9.8m/s²)t² - I figure I need to know "t" before I could solve this.
    Last edited: Jul 5, 2009
  2. jcsd
  3. LowlyPion

    LowlyPion 5,324
    Homework Helper

    Consider what the definition is of acceleration. It is the rate of change of velocity.

    If something starts out at 30 m/s and slows 10 m/s every second, it will reach 0 m/s in how many seconds?

    Here are some formulas for you:

    These lessons might be helpful:
  4. Thanks a bunch. Will get started on the lesson.. then try the problem again.
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