## christine87 2 years ago Solve V = π r2h for h. Show all work. Help?

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1. godorovg

welcome to openstudy

2. christine87

r = 1.35 h = 12.7

3. dan815

hi

4. dan815

why dont you substitute those numbers into the formula and solve it

5. tkhunny

Divide by $$\pi r^{2}$$. $$\left(\pi r^{2}\right)$$ is attached to 'h' via multiplication. Detach it via division.

6. christine87

@dan815 i clearly have done so already, but not coming up with the 'correct' answer according to the rest of the problem i'm inserting it into, hence why I'm seeing if im doing it wrong.

7. christine87

@tkhunny hi ther, thanks, but i'm not trying to solvefor h, i'm subsituting the numbers i posted above. . . seem to be coming up incorrect according to the book/problem set

8. dan815

what is the object you are trying to find the integral of?

9. dan815

volume of* sorry

10. dan815

is it a cylinder?

11. tkhunny

?? "Solve V = π r2h for h" Perhaps we're speaking a different language? One might ask, why are nyou not trying to solve for h? Are you studying Significant Figures"? What answer are you giving that is being rejected?

13. christine87

its a beaker filled with a certain amount of liquid, all a part of a stream of different question s built off this one

14. christine87

@tkhunny because i HAVE h already, as posted above, im trying to find V

15. christine87

this is the complete problem : 5. Calculate the volume of the 50mL graduated cylinder using your measurements of diameter and height, using the formula V = ∏ r2h (r=½ diameter). This is your experimental value. Assuming the accepted value of the volume of the graduated cylinder is 50.00 mL, calculate the percent error of your volume calculation, using the following formula: Percent Error = /accepted value - experimental value/x 100 accepted value

16. dan815

lets compare answers i get for r = 1.35 h = 12.7 pi*2*r*h = 107.725212092

17. tkhunny

That's okay, but I'm really curious how this is consistent with "Solve V = π r2h for h". Anyway, it appears we ARE studying Significant Figures. Now answer the question. What value are you using that is being rejected?

18. dan815

that is area tho i think you mean pi * r^2 *h = 72.7145181618

19. christine87

i'm getting 72.7145. . .but when i plug it into the next step in my problem it doesnt make any sense! im getting a negative percentage error

20. dan815

it says its pir2h so u shud use the other one 107.725212092

21. dan815

your question is wrong i think it shud say pir^2*2 not pi*r2h

22. tkhunny

Well, a negative value isn't possible if you are using the absolute values. Are you using the absolute values? Also, 72.71415 is no good. Use 72.7

23. dan815

pi*r^2 *h |dw:1362879713114:dw|

24. christine87

im totally stumped this is the exact problem taken off the homework, nothing seems to fit

25. dan815

26. dan815

what is your R and H?

27. christine87

@dan815 ok thank you. . .im given D = 2.7 and H = 12.7 and r is 1/2 of D

28. tkhunny

Well, 72.7 mL is a rather horrible approximation for a 50.0 mL beaker. Maybe something else went wrong. Or, maybe we're just testing the %-Errors formula. $$\dfrac{|50.0 - 72.7|}{50.00}\cdot 100\;=\;\dfrac{|- 22.7|}{50.00}\cdot 100\;=\;$$

29. dan815

ok your V = 1.35^2pi*12.7 = 72.7 (72.7-50/50)*100 = ansswer to 2 decimal places

30. dan815

45.43%

31. dan815

u understand?

32. christine87

its a negative number because its the accepted (50) minus the experiemental number, not the other way around thats why im not understanding

33. dan815

wuts a negative number?

34. dan815

is the percentage negative?

35. christine87

the result is negative

36. dan815

oh okay then its -45.43%

37. christine87

how is it possible to have a regative as an answer to this particular question tho?

38. dan815

its possible if its -'ve then it means ur value was 45.43% more than the actual value if its positive then its 45.43% less than the actual value

39. dan815

though i think your question should say do the absolute value of the percentage of error

40. dan815

but if they are defining the percentage of error without absolute value then u can get negative values

41. tkhunny

You are overlooking the Absolute Values. |50.0 - 72.7| = |72.7 - 50.0| = 22.7 There cannot be a negative value resulting from this operation.

42. christine87

ooohh ok i have no idea i havent been taught absolute values, just thrown this problem set today

43. dan815

those 2 lines around the numbers mean take the absolute value so whatever the value they are always take the positive of it

44. christine87

i was given this: Percent Error = /accepted value - experimental value/x 100 accepted value written exactly as it is, no boxes or lines around etc

45. dan815

the equation for absolute value is this |dw:1362882330695:dw|

46. dan815

47. dan815

those / / mean absolute value

48. tkhunny

What are those slanty lines? Those are supposed to be Absolute Value Symbols. Trust me on this.

49. dan815

i wish u were asian right now-_-