Dust Particles Are Pulverized Rock, Which Has Density 2500 Kg/m³

Multiple Choice

Dust particles are pulverized rock, which has density 2500 kg/m³. They are approximately spheres 20 μm in diameter. Treating dust as an ideal gas, what is the root-mean-square speed (thermal speed) of a dust particle at 400°C? (The Boltzmann constant is 1.38 × 10^-23 J/K.)

A) 5.2 × 10^-5 _m/s
B) 1.7 × 10^-5 _m/s
C) 3.0 × 10^-5 _m/s
D) 7.3 × 10^-5 _m/s