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!

HELP! w/ coefficient of kinetic friction problem

  1. Nov 21, 2004 #1

    WCU

    User Avatar

    ok, i have a problem and w/o a given mass i am lost on how to solve it.

    "What is the coefficient of kinetic friction between the ice and the puck in the problem above?"

    problem above states, "A Carolina Hurricanes player hits a puck with his hockey stick during a practice, giving the puck an initial speed of 5.50m/s. The puck decelerates uniformly and comes to rest after traveling 25.0m. What is the rate of acceleration for the puck?"
    -answer is 0.605m/s^2

    Please Help Me!
     
  2. jcsd
  3. Nov 21, 2004 #2
    Why don't you draw yourself a free body diagram of the puck? Try to figure out what forces are working in the horizontal direction. And remember, F = ma.
     
  4. Nov 21, 2004 #3

    WCU

    User Avatar

    yes, i am aware of that, but the MASS is UNKNOWN

    if anyone knows an alternate formula (one that doesn't require mass) i would be most grateful

    thanks for your help...
     
    Last edited: Nov 21, 2004
  5. Nov 21, 2004 #4
    you dont need the mass

    watch

    now that you know the acceleration due to the friction (since the friction force stops it)

    [tex] F = ma = \mu F_{n} = \mu mg [/tex]

    where Fn is normal force of the puck and mu is the co efficient of friction.
     
  6. Nov 21, 2004 #5

    WCU

    User Avatar

    thanks for the help, the formula makes sense, sorta, but i was never taught how to get the normal force without the mass, so i'm still lost, but not as lost

    i do know the answer is 0.0617 ... i just don't know how to get there ...
     
  7. Nov 21, 2004 #6
    normal force without mass?? come again??

    in that equality i have simply used newtons first law that F = ma and frictional force is F = mu Fn = mu mg and equated the two together and eliminate the mass factor
     
  8. Nov 21, 2004 #7

    WCU

    User Avatar

    I thought m = mass... i need the coefficient of friction (u), and i don't have F, Fn, or m ... what units do i use? i feel like the answer is right in front of me and i'm just too blind to see it
     
  9. Nov 21, 2004 #8
    ok realize this FOR ANY FORCE F = ma

    secondly Force of friction = u Fn = u mg (because Force of friction is mg when there is no angle involved)

    now use the first and second lines and you can equate ma = u mg

    a = u g

    u = a / g
     
  10. Nov 21, 2004 #9

    WCU

    User Avatar

    so (0.605m/s^2)/(9.80m/s^2)=u=0.0617, which happens ot be the answer i was looking for.

    thankyou so much
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?



Similar Discussions: HELP! w/ coefficient of kinetic friction problem
Loading...