# Quick question w = ma

1. May 13, 2007

### Aikenfan

1. The problem statement, all variables and given/known data
I have to find the mass of something.... the weight is 358170 lbs

2. Relevant equations

w = ma
a = 9.8m/s2
3. The attempt at a solution
do i convert lbs into kilograms?

2. May 13, 2007

### Hootenanny

Staff Emeritus
Edit: Correction, you should convert lbs (force) into newtons.

Last edited: May 13, 2007
3. May 13, 2007

### Aikenfan

so then what would the unit for the mass be

4. May 13, 2007

### Hootenanny

Staff Emeritus
See the correction in my previous post.

5. May 13, 2007

### Aikenfan

thank you very much

6. May 13, 2007

### Aikenfan

Now that i have mass, I need to find the debroglie wavelength...
so i did wavelength = h/mv

what unit is used for the debroglie wavelength

i have J-s/(Kg)*(km/h)

it should be a distance i believe, so would it be kilometers?

Last edited: May 13, 2007
7. May 13, 2007

### Hootenanny

Staff Emeritus
You need to convert your speed to km/s, then your distance will be in km. However, it is generally best to work in SI units throughout, i.e. m,s, kg etc.

In general the de Broglie wavelength is usually expressed in nm.

8. May 13, 2007

### f(x)

why dont you stick to SI units for a while..that would allow easy substitution of h .
Convert velocity to m/s

9. May 13, 2007

### Aikenfan

10. May 13, 2007

### Hootenanny

Staff Emeritus
You may want to check your conversion from pounds-force to newtons to kilograms.

11. May 13, 2007

### Aikenfan

I used google and it gave me:
(4 293 203.81 N) / (9.8 (m / (s^2))) = 438 082.021 kilograms

12. May 13, 2007

### Hootenanny

Staff Emeritus
Note that pounds-force is not the same as pounds. You need to convert 358170 pounds-force into newtons, then convert this into kg.

13. May 13, 2007

### Aikenfan

358170/9.8 = 36547.959N
= 3 726.854 623 472 kilograms

14. May 13, 2007

### Hootenanny

Staff Emeritus
Again, this is not correct. Type into google "convert pounds force to newtons";

358170 [pounds-force] = 358170 x 4.44822162 [newtons]

15. May 13, 2007

### Aikenfan

358 170 pounds force = 1 593 219.54 newtons

16. May 13, 2007

### Hootenanny

Staff Emeritus
Correct. Now convert that into kg

17. May 13, 2007

### Aikenfan

to Kg = 162573.4224

18. May 13, 2007

### Hootenanny

Staff Emeritus
Beware of rounding errors. I get 162407.7

19. May 13, 2007

### Aikenfan

1 593 219.54 / 9.8 = 162 573.422