A body cools from `100^(@)C` to `70^(@)C` in 8 minutes. If the room temperature is `15^(@)C` and assuming newton's law of cooling holds good, then time required for the body to cool from `70^(@)C` to `40^(@)C` is

Options

A. 14 min
B. 10 min
C. 8 min
D. 5 min

Answer

A

Explanation

`(d theta)/(dt)=k(theta_(av)-theta_(0))`
`(30)/(8)=k(85-15)` . . (i)
`(30)/(dt)=k(55-15)` . . (ii)
`(30)/(8)xx(dt)/(30)=(70)/(40)`
`dt=(8xx70)/(40)=14` min.