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Homework Help: Please help me calculate this resultant force.

  1. May 10, 2009 #1
    The diagram shows a smooth wooden board 30cm long. One end is raised 15cm above the other. A 100g mass is placed on the board. The two forces acting on the 100 g mass are shown in the free-body force diagram.

    what is the magnitude of the resultant force?

    Attached Files:

  2. jcsd
  3. May 10, 2009 #2

    Doc Al

    User Avatar

    Staff: Mentor

    What do you think? Hint: Find components of the weight parallel and perpendicular to the board.
  4. May 10, 2009 #3
    ok erm..

    i was thinking

    mgxsinθ = Frictional force x x

    because since the object is not moving, gravitational potential energy is equals to frictional force?

    please help me my edexcel exams are drawing really near.

  5. May 10, 2009 #4
    btw, x= 30cm
  6. May 10, 2009 #5
    When it says 'smooth' it means that there's no friction.

    The only force on it as far as i can gather is the mgsin(theta).

    So work out the force on it down the plane and from there you can work out acceleration and such, you only ever have to worry about friction if it says 'rough' or gives you a coefficient.

    Edit: Also, out of interest is it the M1 exam you're taking? If so i'd check out this website

    http://math.mdsalih.com/Data/index.php?d=Edexcel+Mathematics/M1 [Broken]

    Many past papers - great practise with mark schemes.

    Good luck.
    Last edited by a moderator: May 4, 2017
  7. May 10, 2009 #6
    nope i'm taking physics unit 1.

    this topic is killing me.

    thanks for the link anyway =)

    ok. so, if there is no frictional force acting on the body,

    so, basically, the only force acting on the object is mgxsin(theta)?

    F = mgxsin(theta)

  8. May 10, 2009 #7

    good luck :D
  9. May 10, 2009 #8
    Hey, no it's not, sorry :P

    no X there, the force isn't dependant on the distance travelled, sorry i didn't read it right :O

    The force here would only be F = mg sin (theta).

    I think the only reason why it gives you those measurements is so that you can work out the angle! Give it a go and see what you get.
  10. May 10, 2009 #9

    oh yea thanks!


    work done = force x distance moved in direction of force

    so, X must not be calculated cuz if X is in, we're calculating work done.

    thanks! =)
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