A body cools from ${50}^0\mathrm{C} \mathrm{to} {49}^0\mathrm{C}$ in 5 sec. How long will it take to cool from ${40}^0\mathrm{C} \mathrm{to} {39}^0\mathrm{C}$? Assume the temperature of surroundings to be ${30}^0\mathrm{C}$and Newton's law of cooling to be valid.

• A

  2.5 s

• B

  10 s

• C

  20 s

• D

  5 s