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: I need help solving three problems (2 for friction, 1 in hooke's law)

  1. Jan 13, 2009 #1
    1. http://www.prep101.com/MCAT/102MCATPhysicsAnswers.pdf [Broken] Numbers 4 7 and 14

    2. As you can see the answers are already available, I'm just having trouble trying to get to them.

    3. For number 4 I've tried plugging in the k value (8000) and distance (.05) in to get a force value. I'm kind of lost from there as I've tried. Number 7 and 14 are kind of the same. However, for 7 I did get the answer when I plugged I plugged it into a Fc = v/r. So I did in fact get 10m/s but when I ignored the squared sign from the original equation (Fc = v^2/r). If I did do something correct then why did the squared sign disappear? For number 14 I don't really know how to tackle this if I don't have mass.

    Once again if you can tell me how to reach the answers to one of these questions that would be great.
    Last edited by a moderator: May 3, 2017
  2. jcsd
  3. Jan 13, 2009 #2


    User Avatar
    Homework Helper

    Welcome to PF.

    In 4 you have determined the force between the 2 blocks. That means that m2 is being accelerated with 400 N. Doesn't that give you then the acceleration for the whole system?

    For 7 I'd say it's coincidence. Work out the equations for mv²/r = μmg. Solve for v and then plug in your numbers.

    For 14 you don't need the mass. F = ma = μmg ... hence a = μg then solve by ordinary kinematic means.
  4. Jan 13, 2009 #3
    Dude thanks so much....I have trouble remembering all the little substitutions you've showed me.

Share this great discussion with others via Reddit, Google+, Twitter, or Facebook