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: How do i find the coefficient of static friction?

  1. Dec 5, 2017 #1
    1. The problem statement, all variables and given/known data
    A coffee cup in your dashboard slides forward when you decelerate from 20 m/s to rest in 3.5 s or less, but now if you decelerate for a longer time. What is the coefficient of static friction between your coffee cup and your dashboard?

    2. Relevant equations
    a = delta a / delta t, Ff = uFn (i think)

    3. The attempt at a solution
    I found out the maximum deceleration needed so that the cup doesn't move (a is < or = to -5.71) but i don't know how to find the coefficient of static friction
    Last edited: Dec 5, 2017
  2. jcsd
  3. Dec 5, 2017 #2


    User Avatar
    Homework Helper
    Gold Member

    1 - I'm not sure why you introduce falling over. The question talks about sliding or not falling..
    2 - When you say "I found the minimum acc..." it would be helpful to show how you did that.
    3 - So, you calculated the acceleration for which the cup slides. Is the acceleration more or less, if you decelerate for a longer time?
    4 - Can you calculate the force on the cup needed to produce this acceleration?
  4. Dec 5, 2017 #3


    User Avatar
    Science Advisor
    Homework Helper
    Gold Member

    It can be important to get this equation exactly right. In fact, there are two, one for static and one for kinetic. Note the difference:
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted