Question

${10}^{23}$ molecules of a gas strike a target of area $1m^2$ at an angle ${45}^o$ to the normal and rebound elastically with speed $1km{s}^{-1}$. The impulse normal to wall per molecule is :
Given: mass of molecule $=3.32\times {10}^{-27}kg$

• A. $4.7\times {10}^{-24}kgm{s}^{-1}$
• B. $7.4\times {10}^{-24}kgm{s}^{-1}$
• C. $3.32\times {10}^{-24}kgm{s}^{-1}$
• D. $2.33kgm{s}^{-1}$

Answer 1

Answer: (A)

$4.7\times {10}^{-24}kgm{s}^{-1}$

Change in momentum $=2mvcos{45}^o$
$=2\times 3.32\times {10}^{-27}\times {10}^3\times \frac{1}{\sqrt{2}}$
$=4.7\times {10}^{-24}kgm{s}^{-1}$