# formula for work & Time ?

by momentum
Tags: formula, time, work
 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 ?
 PF Patron Sci Advisor P: 1,332 The simplest formula for mechanical work (in Physics) is $$W = F s$$ 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? :)
 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 ?
Mentor
P: 40,261

## formula for work & Time ?

$$N_1 R D_1 = W = N_2 R D_2$$

Where: N = number of men; R = rate of work done per man (assumed constant); D = days (or time); W = total work done.
 P: 32 >R = rate of work done per man (assumed constant); what does it mean ? can you give an example of it ? thank you
 Mentor P: 40,261 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: $$N_1 R D_1 = W = N_2 R D_2$$ (20)(R)(10) = (30)(R)($D_2$) Note that the Rs just drop out, and $D_2$ = 20/3 days.
 HW Helper P: 2,640 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".
 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
 PF Patron Sci Advisor Thanks Emeritus P: 38,412 Except that just "work" is meaningless. I prefer Doc Al's "rate of work per day per man".
 P: 2 yes bro u r right for "work" explanation but except tht mine formula is best one

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