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!

A problem involving Force in terms of time?

  1. Mar 2, 2012 #1
    A problem involving Force in terms of time????

    1. The problem statement, all variables and given/known data
    There is a body of 3 kg which is moving to the right with a velocity of 10 m/s. A force of 6 N/s2t2 is applied on the body to the left. How much distane will the body have travelled from t=0 when its velocity is 0 m/s?


    2. Relevant equations
    I think they should be F=ma , dv/dt = a, ds/dt = v


    3. The attempt at a solution
    F=6t2
    So by newton's second law,
    F=3(2t2)=ma
    so i got a = 2t2
    Integrating this, i got v=t3+C and s=t4/4
    Now i thought initial velocity will be -10m/s which i put in C
    and V=0
    so, 0 = t3-10 or t=2.31 seconds
    I have no clue what to do after this. I thought i'll substitute the value of t in the equation with s in it, but some how i don't think its correct. And i don't have any answers to check my solution. please help..
     
  2. jcsd
  3. Mar 2, 2012 #2
    Re: A problem involving Force in terms of time????

    Hint:

    Equation for s has to be written in a different form. With constant acceleration it is

    s = V0t+.5at^2

    You do not have constant acceleration.
     
  4. Mar 2, 2012 #3
    Re: A problem involving Force in terms of time????

    is the equation s=t4/4 + C??
     
  5. Mar 2, 2012 #4
    Re: A problem involving Force in terms of time????

    How about something like this

    s = V0 * t + integral(a(t) * t)*dt

    where a(t) is the acceleration, F(t)/m.

    You have a mistake below for your time

    "Integrating this, i got v=t^3"
     
    Last edited: Mar 2, 2012
  6. Mar 2, 2012 #5
    Re: A problem involving Force in terms of time????

    Your equation s=t^4/4 is incorrect because your previous integration was incorrect.
     
  7. Mar 2, 2012 #6
    Re: A problem involving Force in terms of time????

    But all this mathematics and integration in physics often confuses me. I don't know when to use which technique of integration. Moreover, I have only done the rudiments of calculus. Is there any definite way to know when to use which technique?
     
  8. Mar 2, 2012 #7
    Re: A problem involving Force in terms of time????

    You can use whichever you feel the most comfortable. If you had solved for the time you could use definite integrals and avoid constants of integration.

    When you integrate x^n you get (x^(n+1))/(n+1). Does this help?
     
    Last edited: Mar 2, 2012
  9. Mar 2, 2012 #8
    Re: A problem involving Force in terms of time????

    And when you integrate

    a*x^n you get a*(x^(n+1))/(n+1) where a is a constant. Do you see your mistake now?
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook




Similar Discussions: A problem involving Force in terms of time?
Loading...