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

Homework Help: A kid jumps a meter into the air. How long before he lands?

  1. Sep 27, 2010 #1

    ADH

    User Avatar

    A kid jumps a meter into the air. How long before he lands?

    The answer to this question is .95 seconds.

    I first calculated the time it took for the kid to fall downward. Which was about .45 seconds. But I used the acceleration of 9.8 m/s^2 since he was falling downward. My teachers answer of .95 is assuming that he jumps upward at the rate of 9.8 m/s^2. Is that accurate? I mean, the kid could have jumped up really quickly, but gravity would still pull him down at a rate of .45 sec.

    Thank you for the clarification.

    Also what is this kid's initial velocity? Is it zero?
     
  2. jcsd
  3. Sep 27, 2010 #2
    they don't really give you a whole lot of stuff to work with, but you do know the acceleration of his jump.

    If you looking for time i might try using energy (if you know how).

    Ef - Ei = 0;

    1/2*mv^2 - mgh = 0;

    you can solve for v and that will be your initial velocity.

    Otherwise I would look into the kinematic equations
     
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook