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Formula for work & Time ?

by momentum
Tags: formula, time, work
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momentum
#1
Apr5-06, 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 ?
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jim mcnamara
#2
Apr5-06, 04:33 PM
Sci Advisor
PF Gold
P: 1,381
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? :)
momentum
#3
Apr5-06, 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 ?

Doc Al
#4
Apr5-06, 09:02 PM
Mentor
Doc Al's Avatar
P: 41,306
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.
momentum
#5
Apr5-06, 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
Doc Al
#6
Apr6-06, 07:48 AM
Mentor
Doc Al's Avatar
P: 41,306
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.
Curious3141
#7
Apr6-06, 08:00 AM
HW Helper
Curious3141's Avatar
P: 2,942
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".
chandra rocks
#8
Aug30-10, 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
HallsofIvy
#9
Aug30-10, 08:35 AM
Math
Emeritus
Sci Advisor
Thanks
PF Gold
P: 39,339
Except that just "work" is meaningless. I prefer Doc Al's "rate of work per day per man".
chandra rocks
#10
Aug30-10, 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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