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: I'm pretty sure I'm doing this right . . .

  1. Sep 23, 2010 #1
    1. The problem statement, all variables and given/known data

    A turtle crawls along a straight line, which we will call the x-axis with the positive direction to the right. The equation for the turtle's position as a function of time is
    x(t)=50.0 cm+(2.00cm/s)t-(0.0625 cm/s^2)t^2

    At what time t will the turtle be 10 cm from his initial position for the 1st, 2nd, and 3rd times

    2. Relevant equations

    s(x)= r + v(t) - gt^2

    3. The attempt at a solution

    I have solved already for the first and second times for 6.2 and 25.8. I also figure that it takes 32 seconds to reach the initial point. My reasoning would be 32+6.2 giving me 38.2, but that seems to be wrong. Any help please.
     
  2. jcsd
  3. Sep 23, 2010 #2

    Delphi51

    User Avatar
    Homework Helper

    I don't get the 38.2. Recommend you graph
    y = 2t-0.0625*t^2
    and see when it is 10 or -10.
    Then solve -0.0625*t^2 + 2t -10 = 0
    and -0.0625*t^2 + 2t +10 = 0
    to get the answers more precisely.
     
  4. Sep 23, 2010 #3
    Yeah, I got it. Thanks.
     
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook