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Forces stuff

  1. Jun 30, 2003 #1
    http://cummingsiam.steven-sst.com/force2.jpg

    those are the questions i am having trouble with
    for question 7:
    work is equal to Fscos()
    where
    f = 100 n
    s = 1cm = .01m
    cos() = cos(0) = 1

    work = 100 * .01 * 1
    work = 1 joul?
     
    Last edited: Jun 30, 2003
  2. jcsd
  3. Jun 30, 2003 #2
  4. Jun 30, 2003 #3
    should be fixed now..i added an extra s its force2.jpc not forces2.jpg
     
  5. Jun 30, 2003 #4
    7a
    100N
    7c
    2W
    7b
    Bookwork.

    Yes, work = one Joule.
     
  6. Jun 30, 2003 #5
    The graph given is a F(force)-s(compression) graph. Work done equals area under the straight line. So it isn't 100*0.1*1
     
  7. Jun 30, 2003 #6
    The graph isn't in SI units tho.
     
  8. Jun 30, 2003 #7
    we can change the scale of the x-axis without affecting the result.

    Work done is still area under the straingt line.
    therefore work done = (100)*(0.01)*(0.5)= 0.5 J

    Also unit for work done is Joule, not Newton(N)
     
  9. Jun 30, 2003 #8
    yes, its .5J fpr 7a and 1w for 7c
    i have never worked with force-compression graphs before..but now i know.

    Question 8 i can't do either...
    i don't know the relationship between speed and force...
    force = mass * acceleration is all i know
     
  10. Jun 30, 2003 #9
    #8
    Try to use "energy approach". Kinetic energy is changed to work done to compress the ball. (assume there's no energy loss)
     
  11. Jun 30, 2003 #10
    well, its kinetic energy is .5 * mass * velocity squared
    so .5 * .1(100 grams) * 100(10 squared)
    = 5 jouls

    now..work is measured in jouls..

    now..the graph is linear so we can change the scale to use X to represent both force and compression.

    5j = force * compression *.5
    10 = force * compression
    let X = force and compression
    10 = X squared
    x= square root of 10 = 3.2 (rounded)
    this equals 3.2cm for compression - and converting back our scale we get 320N for our force.
    Thus the maximum compression when the ball hits a wall at 10ms-1 is 32mm

    woooo..that was some tricky stuff.
    But its right.
    320 * .032 * .5 = 5j
    5 = .5 * .1 * v squared
    v squared = 100
    v = 10ms

    its all correct :)
    Thanks
     
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