Question

If three molecules have velocities 0.5, 1 and 2 the ratio of rms speed and average speed is (The velocities are in km/s) 

(A) 0.134 

(B) 1.34 

(C) 1.134 

(D) 13.4

Answer 1

The correct option (C) 1.134

Explanation:

V_rms = √{(V₁² + V₂² + V₃²)/3}

= √[{(0.5)² + (1)² + (2)²}/3]

= √{5.25/3}

V_rms = 1.32 km/s

Also

V_average = {(V₁ + V₂ + V₃)/3}

= {(0.5 + 1 + 2)/3}

= (3.5/2) = 1.16

Hence ratio of rms speed & average speed is

(1.32/1.16) = 1.137