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Force Body Diagram Hamster-

  1. May 17, 2008 #1
    Force Body Diagram Hamster-Please Help!

    1. The problem statement, all variables and given/known data
    A 200 g hamster sits on an 800 g wedge shaped block. The block, in turn rests on a spring scale.

    a) Initially static friction is sufficient to keep the hamster from moving. In this case the hamster and the block are effectively a single 1000g mass and the scale should read 9.8 N. Show that this is the case by treating the hamster and the block as separate objects and analyzing the forces.

    2. Relevant equations

    3. The attempt at a solution
    I am reviewing, and I know I did this problem correctly before, but now it's not working for me. Could someone please tell me what I am doing wrong

    Hamster: I drew a force body diagram, tilting the x & y axes

    Sum of forces on y = Force of Block on hamster - mgcos40=0

    Force of block on hamster = (.200kg)(9.80)(cos40)

    Block: For the block I didn't tilt the coordinates

    Sum of forces on y= normal force - Force of hamster on block in y direction - Mg
    = n - (.200kg)(9.80)(cos40)(cos40) - (.800kg)(9.80)
    n= -8.99 N which is the answer for the second part of the question, when the static friction goes away.
  2. jcsd
  3. May 17, 2008 #2


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    Science Advisor
    Homework Helper

    Hi bcjochim07! :smile:

    You're not asked for the separate friction force at this stage, so just calculate R, the total reaction force (normal + friction).

    That makes only two forces on the hamster … R and mg.

    So R = … ?

    Then use minus R for the block. :smile:
  4. May 18, 2008 #3
    Ok I got it, I forgot that friction has an equal opposite force
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