## IsTim Group Title 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. 11 months ago 11 months ago

1. IsTim Group Title

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

2. IsTim Group Title

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]*** Group Title

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 Group Title

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

5. ***[ISURU]*** Group Title

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

6. IsTim Group Title

1?

7. ***[ISURU]*** Group Title

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 Group Title

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 Group Title

the 102 is suppose to be 10^2

10. IsTim Group Title

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

11. ***[ISURU]*** Group Title

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

12. IsTim Group Title

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

13. IsTim Group Title

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

14. ***[ISURU]*** Group Title

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

15. IsTim Group Title

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

16. ***[ISURU]*** Group Title

@ganeshie8 , @thomaster

17. IsTim Group Title

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

18. ***[ISURU]*** Group Title

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 Group Title

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

20. IsTim Group Title

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]*** Group Title

yo ... that's the missing point!

22. IsTim Group Title

?

23. ***[ISURU]*** Group Title

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

24. IsTim Group Title

But I dunno if those 2 questions are directly related/

25. ***[ISURU]*** Group Title

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

26. ***[ISURU]*** Group Title

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 Group Title

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

28. ***[ISURU]*** Group Title

wt happened ?

29. IsTim Group Title

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

30. IsTim Group Title

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

31. IsTim Group Title

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

32. ***[ISURU]*** Group Title

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

33. IsTim Group Title

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

34. ***[ISURU]*** Group Title

multiply

35. IsTim Group Title

Ok. Thanks.