Question

A body cools from `50^(@)C` to `40^(@)C` in 5 min. The surroundings temperature is `20^(@)C`. In what further times (in minutes) will it cool to `30^(@)C` ?
A. 5
B. `15//4`
C. `25//3`
D. 10

Answer 1

Correct Answer - C
(3) `(Delta theta)/(Delta t) = - k (bar theta - theta_(0))`
`(50 - 40)/(5) = - k ((50 + 40)/(2) - 20)`
`2 = - k xx 25 implies K = - (2)/(25)`
`(40 - 30)/(t) = - k ((40 + 30)/(2) - 20)`
`(10)/(t) = (2)/(25) (15) implies t = (25)/(3)` min