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: Rock Problem

  1. Jan 25, 2006 #1
    I have this one problem solving question that confuses me. Someone pushes a 50kg rock a distance of 10m in a recent competition of strength. The coefficient of friction between the rock and the ground is 0.8 and the person exerts a force of 400 N. I've got my free body digram with my applied force as the force going foward. I know i have to use Fnet to find the amount of newtons but what do i use to find fnet. 400N is suppose to minus with something. I'd appreciate it if someone can bring me a bit further into the question so i can get to the answer. I hope this is enough work, i'm trying to get some review before my exams.
  2. jcsd
  3. Jan 25, 2006 #2
    you'll need to subtract the force opposing the push, ie the friction.
  4. Jan 25, 2006 #3
    so do i multiply 0.8 (coefficient of friction) by 400 N?
    Last edited: Jan 25, 2006
  5. Jan 25, 2006 #4
    ok i got 320N as my force of friction (from ff=uFn ff= 0.8x400N)
    then i use fnet= fapplied-ffriction to get 400-320=80 N
    use fnet in equation fnet=ma
    switch it around a= fnet/m a= 80N/50kg which equals 1.6 m/s2
    am i right? correct me if i'm wrong please, appreciate it.
  6. Jan 25, 2006 #5
    i got the answer now. its 0.16 m/s2 after correcting it.
  7. Jan 25, 2006 #6
    the Fnormal would be the force opposing the weight.
    which, by the way is equal to mg
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook