# Root mean square velocity question

1. Apr 18, 2013

### Insiya

If at 120 K the Vrms is v , then at 480 K it will be

a. 1
b. 2
c. 3
d. 4
Which formula is to be used here? Plz solve this.
1. The problem statement, all variables and given/known data

2. Relevant equations

3. The attempt at a solution

2. Apr 18, 2013

### voko

We don't solve anything here. We can help, but only if you show some effort.

3. Apr 18, 2013

### Insiya

Ok.. but I couldnt understand it.. The formula mentioned in my book is Vrms= radical 3P/density so...What to do next?

4. Apr 18, 2013

### voko

Are you saying there is no equation linking r. m. s. velocity and temperature that you know of?

5. Apr 18, 2013

### Insiya

No.. Im not saying this.. This formula also shows relation with temperature but how to continue..?

6. Apr 18, 2013

### voko

Perhaps you could express how pressure depends on temperature?

7. Apr 18, 2013

### Insiya

Pressure has direct relation with temperature

8. Apr 18, 2013

### voko

What is the equation?

9. Apr 18, 2013

### Insiya

PV=nRT

10. Apr 18, 2013

### voko

Use this and the equation given for r. m. s. velocity to relate the latter with T.

11. Apr 18, 2013

### Insiya

Any clue?

12. Apr 18, 2013

### voko

The clue is in #10. The rest is just algebra.

13. Apr 18, 2013

ok.. Thank U