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: A block with springs and friction

  1. Dec 14, 2008 #1
    1. The problem statement, all variables and given/known data
    A block of mass 5kg is attached to a spring with a spring constant, k = 200N/m, and hangs down so that it rests on a table as shown below.(Sorry no picture) This causes the spring to strech by 10 cm from its equilibrium length. Assume the static coefficient of friction between the table and block is 0.6. An external force, F, is applied in the positive x-direction, as shown.

    b. calculate the force on the block due to the stretched spring.
    d. Calculate maximum force,F, that canbe applied to the block such that the block will continue to remain at rest.
    2. Relevant equations

    3. The attempt at a solution
    b. F=-kx
    F=-200N/m * .1m

    d.5kg*9.81m/s^2 - 20N = 29.05N
  2. jcsd
  3. Dec 14, 2008 #2
    Is it hanging by the spring vertically? and if so I assume the .1m is the displacement from equilibrium position. In which case your answer is seeming correct. the normal determines friction which is W-T (treating spring as a tension force naturally) So your answer should be correct, assuming I understand the question. Do you know if it is wrong or right?
  4. Dec 14, 2008 #3
    The string is vertical and i don't have the answer which is why I'm trying to see if it's right.
  5. Dec 14, 2008 #4
    Your answer, to the best of my knowledge is correct. You properly found the normal and friction is based on the normal. So you are correct
  6. Dec 12, 2010 #5
    I believe this is correct. My only concern that really jumped out at me was that the force due to the spring needed to be subtracted from m*g (force due to gravity) to give a correct value for the normal force.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook