Question

Average kinetic energy of a gas (Molar mass = 4) at "T/2" Kelvin is $8\times {10}^8$ ergs. RMS velocity of the gas at "T/2" Kelvin will be ______ cm/sec.

• A. $2\times {10}^4$
• B. $4\times {10}^4$
• C. $2\times {10}^3$
• D. $4\times {10}^2$

Answer 1

Answer: (A)

$2\times {10}^4$

Formula for kinetic energy is :

$KE=\frac{3}{2}RT$

$3RT=2KE$

$Vrms=\sqrt{\frac{3RT}{M}}$

$Vrms=\sqrt{\frac{2KE}{M}}=\sqrt{\frac{2\times 8\times 10}{4}}$

$=2\times {10}^{4}cm/sec$