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!

Newton's Laws with Friction; Inclines

  1. Aug 9, 2010 #1
    1. The problem statement, all variables and given/known data

    A car can decelerate at -4.80m/s^2 without skidding when coming to rest on a level road. What would its deceleration be if the road were inclined at 13degrees uphill? Assume the same static friction coefficient.

    2. Relevant equations
    Ffr=µkFN


    3. The attempt at a solution
    I am having lots of trouble with friction related problems when the coefficient of static or kinetic friction is involved! But I was thinking...F=ma... F=m(-4.80)...
    Ffr=µkFN= -4.8m=µk(9.80)...really not sure with these types..please help
     
  2. jcsd
  3. Aug 9, 2010 #2

    Doc Al

    User Avatar

    Staff: Mentor

    You're on the right track for finding µs. (Note that it's static friction, not kinetic.)

    Ff = ma
    µsN = ma

    What's the normal force, N? Then you can solve for µs.

    Note that we're assuming the car is accelerating as quickly as possible without skidding, so it's the maximum value of static friction that we want.
     
  4. Aug 9, 2010 #3
    Ffr=ma
    µsN=ma
    µsmg=ma
    µs=4.8/9.80=0.4897? Than Sin(13degrees)*0.4897...??
     
  5. Aug 9, 2010 #4

    Doc Al

    User Avatar

    Staff: Mentor

    Good.
    No.

    Now you have to use what you've found for µs to solve a new problem: what would the car's maximum acceleration be (without skidding) if it were going up that hill? Identify the forces and apply Newton's 2nd law.
     
  6. Aug 9, 2010 #5
    µk(mgCos13deg)+mgSin13deg=a
    (0.489)(9.8Cos13deg)+(9.8)(Sin13deg)=a
    4.669+2.2045=6.87??
     
  7. Aug 9, 2010 #6

    thrill3rnit3

    User Avatar
    Gold Member

    Looks good, except that it's µs because it's static friction and it's negative because it is deceleration.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook




Similar Discussions: Newton's Laws with Friction; Inclines
Loading...