1. Not finding help here? Sign up for a free 30min 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!

Time for a block to come to a stop on a horizontal surface

  1. Oct 1, 2016 #1
    1. The problem statement, all variables and given/known data
    I have a block of mass m on a horizontal surface, which is covered in oil. The tell me the viscous resistance force is a function of the velocity, F(v)=-cv1/2, where I am assuming c is a constant of some kind. I need to find the time that it will take for the block to stop. The initial velocity is V0 at x=0

    2. Relevant equations
    Equations of motion
    Newton's laws

    3. The attempt at a solution
    I thought that I could use ΣF=ma. Then in my equations of motion solve for a=(V-V0)/t
    Since the vertical forces cancel out, the equation would then be:
    -cv1/2=m((V-V0)/t)
    The problem is if I want the block to stop then V will be 0 and my equation doesn't work. Since the resistance is a function of V will I have to integrate it ?
     
  2. jcsd
  3. Oct 1, 2016 #2

    TSny

    User Avatar
    Homework Helper
    Gold Member

    Yes, integrate. The expression (V-V0)/t represents the average acceleration over the time t. You need an expression for the instantaneous acceleration.
     
  4. Oct 1, 2016 #3
    Do I also have to integrate F(V)=-cv^1/2 as well as the acceleration?
     
  5. Oct 1, 2016 #4

    TSny

    User Avatar
    Homework Helper
    Gold Member

    I don't follow. In your equation -cv1/2=m((V-V0)/t) you need to replace the expression (V-V0)/t by an expression representing the instantaneous acceleration.
     
  6. Oct 1, 2016 #5
    as your force is velocity dependent write correct equation of motion
    mass.rate of change of velocity = force and can then proceed further to solve it.
     
  7. Oct 1, 2016 #6
    What I'm asking is do I get the expression for the instantaneous acceleration by integrating the (V-V0)/t with respect to t ?
     
  8. Oct 1, 2016 #7

    TSny

    User Avatar
    Homework Helper
    Gold Member

    No. Just use the definition of instantaneous acceleration.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted



Similar Discussions: Time for a block to come to a stop on a horizontal surface
Loading...