In an hour-glass approximately 100 grains of sand fall per second (starting from rest); and it takes $2 \mathrm{s}$ for each sand particle to reach the bottom of the hour-glass. If the average mass of each sand particle is $0.2 \mathrm{g}$, then the average force exerted by the falling sand on the bottom of the hour-glass is close to
 

• Correct answer
  A

  $0.4 \mathrm{N}$
   
• B

  $0.8 \mathrm{N}$
   
• C

  $1.2 \mathrm{N}$
   
• D

  $1.6 \mathrm{N}$

Hence, the correct answer is option: 'A'.