[MOVED] Cooling time question (solving expo. eqn.)

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willwork4calculushelp

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Newton's law of cooling states that the temperature f (t) of a body at the time t is given by f(t)= To +Ce -kt where C and K are constants amd To is the temperature of the envirnment in which the objects rests. If C = -30.8 and K = 0.05 and t is in hours, how long will it take for a frozen roast to thaw to a temperature of 0 degrees Celsius in a fridge that is at 5 degrees Celsius? Roud to nearest hour.

A. 30 hrs
B. 40 hrs
C. 34 hrs
D. 36 hrs

I have 5 questions similar to this to answer. Can you please show me this one in completion?

Thanks!
 
Well, because we are not a homework service, please show us what you have tried to do.
 
willwork4calculushelp said:
I started like this: f(t)= 5+ (-30.8)-.05
Click to expand...
You need also to plug in the given ending temperature. Also, what happened to the "e to the power of", after the "C" and being the base for the "kt"?

(I will assume that, contrary to standard practice, you mean "K" and "k" to mean the same thing.)

Thank you.

Eliz.
 
willwork4calculushelp said:
f(t)= 5 + -30.8-.05t

Does this look better?
Click to expand...
You've re-inserted the variable "t", but you still need to plug in the given value for the final temperature, and I still don't understand why you've dropped the "e" from the function. Or was the originally-listed function, "T = T<sub>0</sub> + Ce<sup>-kt</sup>" actually meant to be what you're using now, namely "T = T<sub>0</sub> + C - kt"?

Thank you.

Eliz.
 
Im sorry but I do not understand.
I realize that the question is asking how many hours it will take for the roast to reach 0 degrees Celcius if it is in a constant temperature of 5 degrees Celsius.
I can't figure out the right formula for it.
 
willwork4calculushelp said:
I can't figure out the right formula for it.
Click to expand...
But didn't they give you the formula, and you're just plugging in and solving, using techniques you learned back in algebra?

Or did you never learn about exponentials and logarithms back in algebra? If that's the case, then you may need to drop back and take the algebra course that covers this area, because you very much need it in calculus.

Eliz.
 
willwork4calculushelp said:
What does e=?
Click to expand...
Ah. So you haven't studied exponentials or logarithms. Yikes. That's going to make calculus extremely difficult.... :shock:

If you are able to invest the time and effort, you can try to catch up on this material yourself. You'll need to study exponentials (or exponential functions), logarithms, inverse functions, how to graph exponentials and logarithms, and how to solve exponential and logarithmic equations.

(Without this background information, neither this exercise nor its solution method will likely be understandable to you. If you don't know what the natural exponential is, then my telling you to "take the natural log of both sides, apply the log rules, and solve the log equation" will make no sense to you.)

If you would like links to promising sites, please specify.

However, if this study is beyond the time available to you, then you might want to counsel with your academic advisor regarding course placement.

Eliz.
 
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