Question

Four molecules have speeds 2km/sec, 3km/sec, 4km/sec and 5km/sec. The root mean square speed of these molecules (in km/sec) is :

• A. $\sqrt{\frac{54}{4}}$
• B. $\sqrt{\frac{54}{2}}$
• C. $\frac{3}{5}$
• D. $3\sqrt{3}$

Answer 1

The correct option is A $\sqrt{\frac{54}{4}}$

$V_{rms}$ = ${\left[\frac{(2{)}^2+(3{)}^2+(4{)}^2+(5{)}^2}{4}\right]}^{1/2}$ (using standard result)
$=\sqrt{\left[\frac{54}{4}\right]}$