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Homework Help: How do you solve this word problem

  1. Dec 16, 2008 #1
    a rock is thrown vertically upward fom the surface of the moon at a velocity of 24m/s(about 86km/h)reaches a height of s=24t-0.8t^2meters in t seconds.

    (a)find the rocks velocity and acceleration as functions of time?(accleration of gravity on the moon)
    (b)how long did it take the rock to reach its highest point?
    (c)how high did the rock go?
    (d)when did the rock reach half its maximum height?
    (e)how long was the rock aloft?
  2. jcsd
  3. Dec 16, 2008 #2


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    Science Advisor

    well, you can't expect us to solve the problem for you! Here are a few suggestions.

    (a) Find the first and second derivatives of s of course.
    (b) You can find that time by setting the derivative equal to 0 or, conversely, by completing the square in the quadratic function.
    (c) Put the t from (b) in the equation.
    (d) After finding the height in (c), divide by 2, put the s equal to that and solve for t. there will be two solutions, of course.
    (e) Set the height equal to 0 and solve for t. Again there will be two solutions. It should be clear which is the one you want.
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