Solving Newton's Cooling Law Homework

[venger]

Homework Statement

"A cup of hot chocolate, in a room temperature of 21*C, cools accordiing to Newton's law of cooling. Determine the rate of cooling, k, of the hot chocolate if it cools from 86*C to 65*C in 15 minutes"

Homework Equations

Newton's cooling law, ln function
T-Ts=(T. - Ts)e^(kt)

The Attempt at a Solution

T-Ts=(T. - Ts)e^(kt)
65-21=(86-21)e^(15k)
44=65e^(15k)
44/65=e^(15k)
ln(44/65)=15k
(ln(44/65))/15=k
k=-0.02601...
Is this right?

 

[ice109]

Homework Statement

"A cup of hot chocolate, in a room temperature of 21*C, cools accordiing to Newton's law of cooling. Determine the rate of cooling, k, of the hot chocolate if it cools from 86*C to 65*C in 15 minutes"

Homework Equations

Newton's cooling law, ln function
T-Ts=(T. - Ts)e^(kt)

The Attempt at a Solution

T-Ts=(T. - Ts)e^(kt)
65-21=(86-21)e^(15k)
44=65e^(15k)
44/65=e^(15k)
ln(44/65)=15k
(ln(44/65))/15=k
k=-0.02601...
Is this right?

were you taught this formula or the differential equation?

it's right btw