Calculating Helium Vrms and Average KE at 5K

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The discussion revolves around calculating the root mean square speed (Vrms) and average kinetic energy (KE) of helium at 5K. The initial calculations yielded incorrect results, prompting questions about unit conversions and the values used for the Boltzmann constant (kB), temperature (T), and mass (m). A key issue identified was the need to convert atomic mass units (amu) to kilograms for accurate results. After addressing the conversion, the user was able to find the correct answers. The conversation highlights the importance of unit consistency in physics calculations.
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Homework Statement



What is the root mean square speed of Helium at 5K?

Homework Equations



Vrms=sqrt((3kbT)/m)

The Attempt at a Solution



I plugged all the numbers in and keep getting 7.19*10-12. The computer keeps telling me that it is not correct. The next question ask for the avg KE which I found to be 1.04×10−22. I tried using 2/3 Kavg/kb and got 7.21*10-12. The computer tells me that is wrong also. Where am I messing up?
 
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Did you check the units on kB, T, and m? What values did you use for them?
 
That is the whole proble. I remember overhearing the professor and another student talking about converting amu to kg. I plugged in the conversion and got the answer. It has been a long week and day. Guess my brain is still fried from the calculus test tonight. Thanks for the help.
 
Thread 'Variable mass system : water sprayed into a moving container'

Thread 'Variable mass system : water sprayed into a moving container'

Starting with the mass considerations #m(t)# is mass of water #M_{c}# mass of container and #M(t)# mass of total system $$M(t) = M_{C} + m(t)$$ $$\Rightarrow \frac{dM(t)}{dt} = \frac{dm(t)}{dt}$$ $$P_i = Mv + u \, dm$$ $$P_f = (M + dm)(v + dv)$$ $$\Delta P = M \, dv + (v - u) \, dm$$ $$F = \frac{dP}{dt} = M \frac{dv}{dt} + (v - u) \frac{dm}{dt}$$ $$F = u \frac{dm}{dt} = \rho A u^2$$ from conservation of momentum , the cannon recoils with the same force which it applies. $$\quad \frac{dm}{dt}...
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