Calculating Speed of Sound in Helium Gas at 293k

[huykma]

Homework Statement

The speed of sound in fresh water at 293k is 1482 m/s. At what temperature is the speed of sound in helium gas the same as that of fresh water at 293k? Helium is considered a monatomic ideal gas (y = 1.67 and atomic mass = 4.003u).
A)442K
B)377K
C)525K
D)313K
E)633K

Homework Equations

The Attempt at a Solution

Changed equation to --->

Getting really large numbers...

 

[Mike Pemulis]

Check your units. You forgot to do a conversion somewhere.

 

[huykma]

Check your units. You forgot to do a conversion somewhere.

I'm guessing it is the atomic mass that needs to conversion...but I can't seem to find it in my lecture notes... is there an equation for it?

 

[Mike Pemulis]

Good guess. You can look up the definition of an amu on Wikipedia, or Google will just do unit conversions for you. (Type "2 inches in centimeters" and it spits out "5.08 cm." Very handy).

Of course, you still need to know what units to convert amu's into. To figure that out, you can write out all the units on the left-hand side of your last equation, and see what units the atomic mass has to be into get a result in Kelvin. Wikipedia or Google can supply the unit for Boltzmann's Constant if you don't know it.

 

[huykma]

AH I got it, man my professor made this pretty sticky haha. Thanks for the help.

 

[Mike Pemulis]

No problem.