## IsTim 2 years ago In Part A, you determined that the heat added to the coffee is what you got. If it takes 4.2 J of energy to raise the temperature of 1.0 mL of coffee by 1.0∘C, then it should take twice as much energy to raise the temperature of 2.0 mL of coffee by 1.0∘C, or to raise the temperature of 1.0 mL of coffee by 2.0∘C. Multiply carefully to find the total amount of energy needed to raise the temperature of 200 mL of coffee by the required number of degrees.

1. IsTim

This is a hint to an assignment I am currently doing.

2. IsTim

I haven't read thru the textbook much or my notes; I'ved tried, and instead made a formula sheet, although I don't know what formula to apply to this.

3. ***[ISURU]***

use $E = mc \theta$ Since there r lot of data this one can be use easily ... I think u should be familiar with this...

4. IsTim

Actually, haven't seen this in my formula sheet. But I'll try it out.

5. ***[ISURU]***

wt's the value of "required no.of degrees" mentioned in the question ?

6. IsTim

1?

7. ***[ISURU]***

then I think u can use a relationship with ratios to solve this one cause the problem says "Multiply carefully to find " which mean question doesn't expect use of any formula instead it expect to build the answer from given data... change of 1 degree in 1ml = 4.2 J change of 1 degree in 2ml = 8.4 J change of 1 degree in 200 ml = 8.4*100 J

8. IsTim

These are the answers that I gave to the work, which it stated was incorrect. It requires 3 significant figures. Submitted Answers ANSWER 1: Deduction: -3% "what you get" = 8.4⋅102 J ANSWER 2: Deduction: -3% "what you get" = 8.40⋅102 J

9. IsTim

the 102 is suppose to be 10^2

10. IsTim

So yes, I did use your answer, but apparently it was incorrect here.

11. ***[ISURU]***

It requires 3 significant figures. = is it same for the 840 J ?

12. IsTim

wouldn't 8.40*10^3 J have worked?

13. IsTim

Because 840 is only 2 sig digs without using a decimal point

14. ***[ISURU]***

no .. I just told that 'cause it's the same answer I get even if I use E = mc*theta

15. IsTim

So, both answers would be considered incorrect with this question then?

16. ***[ISURU]***

@ganeshie8 , @thomaster

17. IsTim

I managed to get the question after that correct, if it helps at all.

18. ***[ISURU]***

if 840 J is wrong .... there is one possible reason: we calculate 840 J to a temp. change of 1 degree. But the question asks the energy need for a temp. change of required no. of degrees. And we assume that is also as 1 degree. But this question has a section name part A. Does that part mention about some reading of temperature regarding this coffee cup

19. IsTim

Yes. This is a 'hint' to a larger question.

20. IsTim

Suppose that you have left a 200-mL cup of coffee sitting until it has cooled to 30∘C , which you find totally unacceptable. Your microwave oven draws 1100 W of electrical power when it is running. If it takes 45 s for this microwave oven to raise the temperature of the coffee to 60∘C , what is the efficiency of heating with this oven? Find the efficiency e of the oven. You will need to use the fact that 4.2 J of energy is required to raise the temperature of 1.0 mL of coffee by 1.0∘C .

21. ***[ISURU]***

yo ... that's the missing point!

22. IsTim

?

23. ***[ISURU]***

the temperature of the coffee cup was 30 degree at the beginning and it has to be increased up to 60 degree

24. IsTim

But I dunno if those 2 questions are directly related/

25. ***[ISURU]***

So we must calculate energy need to change the heat of 200ml by 30 degree

26. ***[ISURU]***

not just by one degree which is 840 J instead it should be 8.4*30 * 100 J which is 252*100 J and it also satisfy the condition of 3 digit ... try that one!

27. IsTim

I've got 2 tries left. i'll test it out

28. ***[ISURU]***

wt happened ?

29. IsTim

err sorry. i'm asking this question on several different mediums, and i'm just 'cross referencing'

30. IsTim

Err, 8.4*30 * 100 J looks like $8.4*10*100$ 252*100 J looks like $252*100$

31. IsTim

Because if that was true, wouldn't that make the question incorrect?

32. ***[ISURU]***

srry.. could u explain it more ... it's not clear

33. IsTim

The stars; do they represent the 'multiply' or the 'exponent' function?

34. ***[ISURU]***

multiply

35. IsTim

Ok. Thanks.