Does Doubling Gas Molecules Affect RMS Speed?

[ajmCane22]

Homework Statement

An ideal gas is kept in a container of constant volume. The pressure of the gas is also kept constant
(a) If the number of molecules in the gas is doubled, does the rms speed increase, decrease, or stay the same?
(b) If the initial rms speed is 1300 , what is the final rms speed?

Homework Equations

PV=nRT...I think

The Attempt at a Solution

For part I, I believe the rms speed decreases. So if the only thing changing is the number of molecules wouldn't doubling the molecules cause rms to decrease by half? I know the answer is no, because the computer said so, I'm just not sure why it's wrong. And how much does it decrease then?

 

[willem2]

If the volume and the pressure must remain constant, the only way to get in more molecules is cooling the gas, and let in more gas to keep the pressure constant.

If the original tempererature was T, what is the new temperature?

After you've found it use

$$v_{rms} = \sqrt { \frac {3 R T} {m} }$$

where m is the mass of one mole of the gas molecule