Question

Please anyone help me!!

Answer 1

When a cold drink is taken from a refrigerator, its temperature is 5°C.
After 25 minutes in a 20°C room its temperature has increased to 10°C.
(a) What is the temperature of the drink after 50C minutes?
(b) When will its temperature be 15°C?

Answer 2

http://answers.yahoo.com/question/index?qid=20090326150117AA7jVrX :)

Answer 3

@Cha1234 That question is asking for different values.

Answer 4

but this site has really confused answer

Answer 5

can anyone explain this to me here?

Answer 6

I learned this in basic physics, I assume solving the same way.
Have you been taught Newton's Law of Cooling?\[\frac{ dT }{ dt }=k(T-20)\]

Answer 7

can anyone explain this to me that how I m getting this answer ln[(20 - T)/(20 - 5)] = - 0.01622

Answer 8

when I m calculating it I m getting 1.10623

Answer 9

don't make it so hard
it is easier than you think

Answer 10

When a cold drink is taken from a refrigerator, its temperature is 5°C. After 25 minutes in a 20°C room its temperature has increased to 10°C.
(a) What is the temperature of the drink after 50C minutes?
(b) When will its temperature be 15°C?

Answer 11

work with the differences in the temperature, that is what decays to zero
initial difference is \(20-5=15\) degrees, after 25 minutes the difference is \(10-20=10\) degrees so the difference has decreased by \(\frac{10}{15}=\frac{2}{3}\)

Answer 12

i.e. every 25 minutes, the difference in the temperature decreases by \(\frac{2}{3}\)
starting with an initial difference of \(15\) you can model this by
\[15\left(\frac{2}{3}\right)^{\frac{t}{25}}\]

Answer 13

after another 25 minutes, at 50 minutes, it will decrease by another \(\frac{2}{3}\) from \(10\) to \(10\times \frac{2}{3}=\frac{20}{3}=6\tfrac{2}{3}\)

Answer 14

that of course means it is \(6\tfrac{2}{3}\) colder than the 20 degree room, so its temperature is \(20-6\tfrac{2}{3}=13\tfrac{1}{3}\)

Answer 15

b) when will it be 15 degrees?
that means
b) when will it be 5 degrees colder than the room

set
\[15\left(\frac{2}{3}\right)^{\frac{t}{25}}=5\] and solve for \(t\)