**(a) **Rms speed:

$\overline{){{\mathbf{v}}}_{\mathbf{r}\mathbf{m}\mathbf{s}}{\mathbf{=}}\sqrt{\frac{\mathbf{3}\mathbf{R}\mathbf{T}}{\mathbf{M}}}}$

For Helium, M = 4g = 4 ×10^{-3} kg, R = 8.314 J/mol K (gas constant), and T = 0 + 273.15 = 273.15 K.

Substituting:

(a) Calculate the rms speed of a helium atom at 0°C.

(b) Determine how many times per second it would move back and forth across a 7.0 m long room on the average, assuming it made very few collisions with other molecules.

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