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Homework Help: Lots of physics problems

  1. May 28, 2004 #1
    i took physics class by correspondance so i can get a better grade, now i have a few few per module (modules consists of over 50 odd questions), please just point me in the right direction and i'll do the rest, thx, some may seem pathetic though, but i want to get good marks so i dont want any question un-answered


    1b: a box has 3 ropes tied to it, 3 guys exert the following forces.
    F1= 220N at 90degrees
    F2= 185N at 162degrees
    F3= 235N at 280degrees
    determine magnetude and direction of the box.

    5c: a marble with mass of 32g at speed of 24cm/s hits directly at a stationary smaller glass marble with mass of 15g, after glass marble moves with speed of 30cm/s
    if collision perfectly elastic, determine the velocities of both marbles.

    Module 3

    3: a charged object(qa=-3.6uC) is a corner af a right triangle, (qb=+2.5uC, 2m due east of qa) and (qc=+2.5uC, 2m due south of qa)
    i found the resulting force Fr=4,09x10power of -4 N
    now i have to find the angle, but since its a decimal i cant do sin-1 on my calculator, any help

    4d: a charged bal is suspended by an insulated thread, 45cm from a source charge. with this info (gravity(g), the angle(o), and mass(m)) derive an equation to find Ft(force of tension by thread).
    i came up with Ft=mg x cos(o)

    5:a dust spec is in a electric field, E=2.50N/C to the right, dust spec has a charge of +13uC and mas of 5.25mg
    i found the accelaration, but i cant find the direction with calculation, only by comon sens.

    Module 4

    these ones are iffy, try not to give me the answer

    2a: an electron is in an electric field, he travels from one plate to the other, what type of motion, suport answer with Newtons law.
    that is the direct question, tell me what you can

    3c: a positivly charged particle enters an electric field horizontaly and it is atracted by one of the plates
    what type of motion, suport answer with Newton's law.
    same deal here, this is the exact question

    Module 5

    5:the repulsive force between 2 ceramic magnets was mesured and found to be determined by distance (no it doesnt sayhaha sercasm)
    distance (mm) force(N)
    10 3.93
    12 0.40
    14 0.13
    16 0,057
    18 0.03
    20 0.018.........and on and on
    the question is: does this follow an inverse square law, support with calculations.
    i dont know the meaning of inverse square law, and i dont know what calculations to use

    Module 6

    3b: an aluminum plane is flying due west parallel to the ground at 350m/s, wing span 22m, erth magnetic field 8.30x10to power of -5 T
    which wing would be negetively charged, suport answer with diagram. i did every diagram possible, but i dont know how to find the charge.

    1a: following statement either incomplete or false, rewrite each statement
    the source of all electromagnetic radiation is and accelerating particle.

    Module 7

    5:in early Millikan experiment, he observed that the following measured charges , among others, appeared at different times on a single oil drop, what value of elementary charge can be deduced from this data?
    a 6.65 x 10powerof-19C
    b 8.204 x 10powerof-19C
    c 11.5 x 10powerof-19C
    d 13.13 x 10powerof-19C
    e 16.48 x 10powerof-19C
    f 18.08 x 10powerof-19C
    g 19.71 x 10powerof-19C
    h 22.89 x 10powerof-19C
    i 26.13 x 10powerof-19C
    i need to set up a chart, and i should explain the rational behind each calculation, but i dont know where to start.

    5:sun taning produces cell damage in the skin, why is UV light capable in doing so, and not infrared radiation

    6: certain types of black-and-white film are not sensitive by redlight, they can be devloped usinf red safe light, explain this on basis of photon theory of light.

    Module 9.............. still to come.

    take your time, take a day or 2 thx in advance
  2. jcsd
  3. May 29, 2004 #2


    User Avatar

    Wow, did you leave out any problems in the book? For question 1b, a simple application of a force diagram should help you out. Break up the forces into components, and add up the x and y component pieces. That'll tell you the direction of the acceleration, but not necessarily it's displacement(say if the box were initially moving)

    5c is easy since it has all the information needed to use only momentum conservation without having to invoke work energy theorem, even though the problem mentioned the collision to be elastic.

    the rest of your questions i'll leave to you, its 2:30 am, and i'm a little drunk right now, plus I have a study group at like 7 am, so good luck! :approve:
  4. May 29, 2004 #3
    2a and 3c: What does the electric field 'look' like between the two plates? How does its magnitude change, if it does at all, when you go from one plate to the other? Does it change at a constant rate, or maybe is it constant along the way? You surely know the relation between the electric field, the electric force and the charge of the particle -- F = Eq. So if you know how the electric field E 'behaves', you also know how the electric force F does. And from there it's just a simple analysis of a body's motion under one force.

    5. http://hyperphysics.phy-astr.gsu.edu/hbase/forces/isq.html
    In other words, you want to prove that the force of repulsion is proportional to the inverse square of the distance:
    [tex]F(x) = \frac{C}{x^2}[/tex]
    Where C is some constant. To prove this, pick one row of data, for example 10mm and 3.93N. Without forgetting to change 10mm into meters, put these values in the equation above and find the value of C. Now go back to the data and see if this holds for the rest of the rows -- divide the constant by the square of the distance and see if it equals the force.

    I'll try to answer more questions when I have more time, I'm studying for an exam myself right now. :) Good luck.
    Last edited: May 29, 2004
  5. May 29, 2004 #4
    for question 2a and 3c, no calculation is needed, or else i would of done it myself, it asks the identify the type of motion while refering to Newtons law, although i did answer these, i wanted to make sure i had them right
  6. May 29, 2004 #5
    Were have I mentioned performing calculations? The particles act as if they were balls that were free thrown in air while being subject only to gravity. The electron behaves like a ball that was thrown with either no velocity or vertical speed only (the problem does not say), and the positively charged particle behaves like a ball that was thrown with horizontal speed only. And I haven't even taken out my calculator.
    Last edited: May 29, 2004
  7. May 29, 2004 #6
    This is why i want to take correspondants, all you do is fill in the questions they tell you they are marking, get someone to help if you need too, make sure every one is right, and then mail it too them, and recieve 100% consistently. Kinda cheap, but when universities ask for ridiculous averages, this is what they get lol...
  8. May 29, 2004 #7
    i have a problem with english terminology, and i'm french, and i learnt this stuf in french, so most of the questions are because i cant understand them
  9. May 31, 2004 #8
    i'm done all of this so dont need no more help, thx guys
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