# Formula for work & Time ?

1. Apr 5, 2006

### momentum

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. Apr 5, 2006

### Staff: Mentor

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? :)

3. Apr 5, 2006

### momentum

no....there is no physics involved in it.

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. Apr 5, 2006

### Staff: Mentor

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

Where: N = number of men; R = rate of work done per man (assumed constant); D = days (or time); W = total work done.

5. Apr 5, 2006

### momentum

>R = rate of work done per man (assumed constant);

what does it mean ?

can you give an example of it ?

thank you

6. Apr 6, 2006

### 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:

$$N_1 R D_1 = W = N_2 R D_2$$
(20)(R)(10) = (30)(R)($D_2$)

Note that the Rs just drop out, and $D_2$ = 20/3 days.

7. Apr 6, 2006

### Curious3141

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. Aug 30, 2010

### chandra rocks

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. Aug 30, 2010

### HallsofIvy

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

10. Aug 30, 2010

### chandra rocks

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