Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Help with Kinematics Physics problem

  1. Dec 6, 2004 #1
    Planet X.

    Toss rock straight up in air at 17 m/s (initial speed).
    After 14.2, the rock is falling towards him at 8.56 m/s

    What is magnitude of the local gravitation acceleration?

    Can someone show me how to do this, OR show me the equation for solving this type of problem? thanks

    In terms of showing work, I can't even find an equation or an approach that I would be confident handing in as an answer, so I haven't gotten past the "how I approach this" point in the problem.
    Last edited: Dec 6, 2004
  2. jcsd
  3. Dec 6, 2004 #2

    this is just about all you need to know to solve this problem...a first order linear differential equation with constant coefficients (remember signs)
  4. Dec 6, 2004 #3


    User Avatar
    Science Advisor
    Homework Helper

    The formula is the correct one and the problem is simplified assuming constant gravitation field of intensity "g".Then
    [tex] g=\frac{v_{0}+v_{f}}{t}} [/tex] which gives exactly 1.8 a bit more than the value on the moon.
  5. Dec 6, 2004 #4
    What units would the answer be in? I want to double check and make sure I got it right.
  6. Dec 6, 2004 #5


    User Avatar
    Science Advisor
    Homework Helper

    I specifically left it without uniits,because i thought u specifically left time without units in the problem's text itself.It was some sort of a "payback".If those are seconds (it makes sense to think that way,in any unit system time's unit is second),then [itex] g=1.8\frac{m}{s^2} [/itex].If those were hours/days,then the assumption of constant gravitational field would not hold and the problem would be more compplicated than the author wanted.Or it could hold,but the intensty would be vanishingly small...
  7. Dec 6, 2004 #6
    erm, my bad, it is 14.2 seconds I must of missed it when copying the problem :/
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook