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Hi all. Need guidance for some fundamentals physics

  1. Jun 30, 2014 #1
    Hi everyone.
    I am self studying for my GCE for the past 6 months now. I have been doing revision for a long time and did some question papers. I have a few problems and hope the people here can guide me. Thank you

    Problem 1.
    1. The problem statement, all variables and given/known data
    A 5.0kg mass is suspended from the ceiling. A horizontal force F is applied to hold the string in position as shown

    http://i.imgur.com/ZdR72ff.jpg

    Determine the reading of F on the spring balance by using a scale diagram

    2. Relevant equations

    None

    3. The attempt at a solution

    http://i.imgur.com/2KO2AnT.jpg
    Am I doing it correctly?
    It doesn't really make sense to me. I can't determine the force F. I only have 30degree angle and the weight.

    Problem 2
    1. The problem statement, all variables and given/known data
    A ladder weighing 200N is being held by a man. The man shoulder acts as a pivot. His arm is pushing an upward force F.

    http://i.imgur.com/dMrcRtK.jpg

    Where could a weight of 150N be hang upon, so that force F do not need to counteract the weight of the ladder

    2. Relevant equations
    Moment= F x Perpendicular Distance

    3. The attempt at a solution
    I am not sure if I am understanding it correctly. If I am not wrong, the question is asking me, where can I hang a weight of 150N, so that force F no need to counteract the weight of the ladder. Meaning, assume force F = 0N.

    Let the distance be x
    Total clockwise moment = total anti clockwise moment
    150x = 200*0.5
    150x = 100
    x = 2/3
    = 0.667m.

    Therefore it needs to be hang 0.667m away from the pivot or at 3.167m of the ladder.

    Am I understanding this correctly?

    Problem 3
    1. The problem statement, all variables and given/known data

    The figure shows 2 terminals M and N of a potential divider connected to a 6V battery. The circuit is connected to a Cathode-ray Oscillator.

    http://i.imgur.com/zeV2e3j.jpg

    (a) Describe in details what happens as the terminal is moved at a uniform speed from N to M.
    (b) Draw the final reading of the final trace that is shown the CRO as N is moving towards M.

    2. Relevant equations

    None

    3. The attempt at a solution

    (a) As terminal N is moving towards M, there will be an increased in e.m.f, the results in a higher reading on the tracd

    (b) http://i.imgur.com/bldLWjF.jpg
    This is my attempt.

    Please correct me if I make any mistakes thank you.

    Theoretical Problem:
    Is the work done the same if I move an object vertically upwards of height 2.0m v.s moving up a ramp at height until it reaches 2.0m?

    From what I memorise, they are the same. Am I right? But can someone explain why? I want to understand why.

    Thank you!
     
  2. jcsd
  3. Jun 30, 2014 #2

    jedishrfu

    Staff: Mentor

    Welcome to PF!

    The first thing you should do is separate each of these problems out into separate threads as its very hard and confusing to get help when its tangled together with other problems.

    On the first problem try drawing a force diagram, in this example the forces should add up to zero. One force is the pull of gravity on the weight, the second is the pull from the string attached to the ceiling and the third is the force from horizontal string. I'd review some examples from other problems to see how its done.
     
  4. Jun 30, 2014 #3

    berkeman

    User Avatar

    Staff: Mentor

    I will have the OP post these questions one at a time in separate threads. This thread is closed.
     
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