A cup of coffee was prepared at 90 degree C and left in a room at 20 degree C. Now the temperature is 60 degree and it is cooling at 1 degree/min. How much time has past since the coffee was made.
? netwons law ? dont know how to start it :S
A cup of coffee was prepared at 90 degree C and left in a room at 20 degree C. Now the temperature is 60 degree and it is cooling at 1 degree/min. How much time has past since the coffee was made.
? netwons law ? dont know how to start it :S
let y = temperature at any time t
$\displaystyle \frac{dy}{dt} = k(y - 20)$
at $\displaystyle y = 60$ degrees, $\displaystyle \frac{dy}{dt} = -1$ deg/min
$\displaystyle -1 = k(60 - 20)$
$\displaystyle k = -\frac{1}{40}$
$\displaystyle \frac{dy}{dt} = k(y - 20)$
separate variables and solve for y as a function of t ... you have k and you also know y(0) = 90