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Formula for work & Time ?

  1. Apr 5, 2006 #1
    Hi,

    whats the formula for work and Time ?


    is it this ?

    N1 * D1 * W1 =N2*D2*W2

    where ,
    N1=No of Persons
    D1=No of days
    W1=work


    N2=No of Persons
    D2=No of days
    W2=work


    is thats formula correct for work and time ?
     
  2. jcsd
  3. Apr 5, 2006 #2

    jim mcnamara

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    Staff: Mentor

    The simplest formula for mechanical work (in Physics) is
    [tex] W = F s [/tex]
    Here, the force is contant and parallel to displacement and the body moves in a steady direction. W is work, F is force and s is displacement. The result is in Joules.

    Unless you want manhours? What exactly are you trying to do? :)
     
  4. Apr 5, 2006 #3
    no....there is no physics involved in it.

    i'm talking about maths.

    problems like...."20 man works for 10 days did a work, how long it would be taken by 30 man"?

    this kind of problem

    whats the formula ?

    I have forgotten the formula....is it like same as i posted ?
     
  5. Apr 5, 2006 #4

    Doc Al

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    Staff: Mentor

    [tex]N_1 R D_1 = W = N_2 R D_2[/tex]

    Where: N = number of men; R = rate of work done per man (assumed constant); D = days (or time); W = total work done.
     
  6. Apr 5, 2006 #5
    >R = rate of work done per man (assumed constant);

    what does it mean ?

    can you give an example of it ?

    thank you
     
  7. Apr 6, 2006 #6

    Doc Al

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    Staff: Mentor

    Don't treat this as some esoteric formula from the ancients. It should be just "common sense", a variation of "Distance = Rate X time".

    An example of R would be: a man can lift 50 bales of hay per day, so R = 50 bales/day/man.

    So, if one man can lift 50 per day, how much total can be lifted in 3 days by 5 men?

    Using W = N R D gives, W(total) = (5 men) (50 bales/day/man) (3 days) = 750 bales

    But to solve a problem like " if 20 men working 10 days did a certain amount of work, how long would it take 30 men to do the same work?" you don't have to know R. Just use:

    [tex]N_1 R D_1 = W = N_2 R D_2[/tex]
    (20)(R)(10) = (30)(R)([itex]D_2[/itex])

    Note that the Rs just drop out, and [itex]D_2[/itex] = 20/3 days.
     
  8. Apr 6, 2006 #7

    Curious3141

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    Homework Helper

    Those are the dumbest of word problems. I would be tempted to answer : "The job would never get done, because the extra men would entice the entire lot to unionise and strike for better pay and conditions".
     
  9. Aug 30, 2010 #8
    this is correct
    N1 * D1 * W2 =N2*D2*W1
    where ,
    N1=No of Persons
    D1=No of days
    W1=work


    N2=No of Persons
    D2=No of days
    W2=work
     
  10. Aug 30, 2010 #9

    HallsofIvy

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    Staff Emeritus
    Science Advisor

    Except that just "work" is meaningless. I prefer Doc Al's "rate of work per day per man".
     
  11. Aug 30, 2010 #10
    yes bro u r right for "work" explanation but except tht mine formula is best one
     
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