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: Find the acceleration in terms of friction

  1. Nov 29, 2008 #1
    1. The problem statement, all variables and given/known data

    A block of mass m lies on a horizontal table. The coefficient of static friction between the block and the table is µs. The coefficient of kinetic friction is µk, with µk < µs.
    Suppose you push horizontally with precisely enough force to make the block start to move, and you continue to apply the same amount of force even after it starts moving. Find the acceleration a of the block after it begins to move.

    2. Relevant equations

    3. The attempt at a solution
    The answer to this example is a=µsg-µkg.
    I am very confused on problems in which both kinetic and static friction are given. Can someone explain to me what this statement means? If the object is moving, why are we subtracting kinetic from static, should the kinetic be greater at this point?
  2. jcsd
  3. Nov 29, 2008 #2


    User Avatar
    Science Advisor
    Homework Helper
    Gold Member

    I don't believe you have clearly understood the problem. It is given that a force is applied to the block that is ju-u-u-st enough to get it to move. I mean like if it was just an iota less, it wouldn't move. What is the magnitude of that force? Once you establish it, that same force continues to be applied to the object. What is now the NET force acting on the moving object ? (remember that the block is moving, so kinetic friction is working agin' ya). Once you identify the NET force, solve for the acceleration using Newton 2.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook