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 with force problem

  1. Nov 28, 2013 #1
    1. The problem statement, all variables and given/known data

    A mass "b" is placed on top of a larger mass that is 2.4 times the mass of the smaller one as shown. The coefficient of friction between the larger block and the surface is 0.35. A horizontal force acts on the larger block.

    a) What force would be necessary to maintain an acceleration of 4.0 m/s2? (in terms of "b")
    b) What would be the minimum coefficient of static friction necessary to keep the smaller block from slipping?

    2. Relevant equations

    a = Fnet / m
    Ff = µFN
    Fnetx = Fa + Ff
    Fnety = Fg + FN

    3. The attempt at a solution

    Fg = ma
    Fg = 3.4b (9.81)
    Fg= 33.354b N [down]

    Fnety = Fg + FN
    0 = 33.354 N [down] + FN
    FN = 33.354b N [up]

    Ff = µFN
    Ff = (0.35)(33.354b N)
    Ff = 11.6738b N

    Fnetx= Fa + 11.6738b N

    I don't know how to get Fnetx from here, and I don't know if this is right so far


    4.0 m/s2= Fnet / 3.4b

    Also I don't understand part b)
    Thanks for the help
     
  2. jcsd
  3. Nov 29, 2013 #2

    haruspex

    User Avatar
    Science Advisor
    Homework Helper
    Gold Member
    2016 Award

    No, Fnetx = Fa. You want to find Fapp, where Fnetx = ƩF = Fapp + Ff.
    The smaller mass is to accelerate at 4m/s2. What force is necessary to achieve that? Where is that force coming from?

    Btw, I recommend working entirely symbolically, only plugging in numbers when you get to the final equation. It makes it easier to find errors, and much easier for others to follow.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted



Similar Discussions: Help with force problem
Loading...