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Formula for work & Time ? 
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#1
Apr506, 01:30 PM

P: 32

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
Apr506, 04:33 PM

Sci Advisor
PF Gold
P: 1,382

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? :) 


#3
Apr506, 08:45 PM

P: 32

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 ? 


#4
Apr506, 09:02 PM

Mentor
P: 41,454

Formula for work & Time ?
[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. 


#5
Apr506, 11:36 PM

P: 32

>R = rate of work done per man (assumed constant);
what does it mean ? can you give an example of it ? thank you 


#6
Apr606, 07:48 AM

Mentor
P: 41,454

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. 


#7
Apr606, 08:00 AM

HW Helper
P: 2,950

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".



#8
Aug3010, 04:02 AM

P: 2

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 


#9
Aug3010, 08:35 AM

Math
Emeritus
Sci Advisor
Thanks
PF Gold
P: 39,533

Except that just "work" is meaningless. I prefer Doc Al's "rate of work per day per man".



#10
Aug3010, 09:03 AM

P: 2

yes bro u r right for "work" explanation but except tht mine formula is best one



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