1. ## serium

Dear Sir
I would be grateful if you can help me to solve the the below questions
I managed to get the answer to part (a) but cannot get the time 11.16 minutes in part b

thanks
Kingsman

I

2. Originally Posted by kingman
Dear Sir
I would be grateful if you can help me to solve the the below questions
I managed to get the answer to part (a) but cannot get the time 11.16 minutes in part b

thanks
Kingsman

I
This is a seperable differential equation with solution:

$x=10+Ae^{-t/50}$

As $x(0)=20$, we have $A=10$

so:

$x=10(1+e^{-t/50})$

To find when $x(t)=18$ we solve:

$10+Ae^{-t/50}=18$

which has solution:

$t=-50 \ln(0.8)=11.16$ minutes (rounded to two places of decimal)

CB