1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
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: Explain Displacement problem

  1. Mar 8, 2008 #1
    Hi friends am new to Physics. Am facing a problem while caculating displacment.

    Acceleration of free falling object is 9.8m/s/s. Am using formula 1/2*b*h to get the displacement.According to me if object acceleration is 9.8 m/s/s then after 1 second it's displacment should be 9.8 meters and after 2 second it should be positioned at 29.4 m.
    If i use the formula to calculate displacment then it is positioned at 4.9 m at end of 1st second and a the end of 2nd second it 19.6 m. Please explain why object is positon at 4.9 m by using this formula.

    At t = 1 s
    d = (0.5) * (9.8 m/s2) * (1 s)2 = 4.9 m

    At t = 2 s

    d = (0.5) * (9.8 m/s2) * (2 s)2 = 19.6 m

    At t = 5 s

    d = (0.5) * (10 m/s2) * (3 s)2 = 44.1 m

    For refrence see http://www.glenbrook.k12.il.us/gbssci/phys/Class/1DKin/U1L5d.html [Broken]
    Last edited by a moderator: May 3, 2017
  2. jcsd
  3. Mar 9, 2008 #2
    The statement in red is totally wrong.It also depends on the initial velocity of the object from which it was thrown downwards.
    NOW for the hint part:

    It seems you are confused with the formula part.
    The formula s=1/2 at^2 [u=0] does not give the displacement in that particular time interval,in fact It gives ya the total displacement from the initial time interval.
    To get the displacement in a particular time interval you must calculate the displacements using the formula and substituting the correct values and then calculate the difference.
    Last edited by a moderator: May 3, 2017
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook