1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Homework Help: Convert the diameter to inches or to feet

  1. Nov 21, 2014 #1
    1. The problem statement, all variables and given/known data
    Convert the diameter to inches or to feet. Inches = 28 feet*12 inches/foot + 4 inches = 340 inches. Feet=28.333

    Radius = 170 inches or 14.167 feet.

    Area of the bottom in square inch = 3.1416*170*170 = 90,746 sq in

    Area of the bottom in ft2 (square feet) = 3.1416 *

    2. Relevant equations

    3. The attempt at a solution
    Inches equals 28 times 12 plus 4 = 340

    Feet is 28 +1 divide by 12 times 4 =28.333

    The area of the bottom in inches is 3.1416 times 170 times 170= 90,746

    The area in feet would be 3.416 times 28.333 times 28.333 = 2521.947
  2. jcsd
  3. Nov 21, 2014 #2

    Simon Bridge

    User Avatar
    Science Advisor
    Homework Helper

    I take it you are charged to write 28'4" either as feet or inches instead of a mixture?
    Check: is this a diameter or a radius?

    Some notes:

    28+(4/12) feet is all you need ... that's 28.1/3 feet.
    [note 1 divide by 12 times 4 is the same as 4/12]

    The area of the bottom cannot be measured in inches - since "inches" is the unit of length, not area.
    You can also convert square inches to square feet by realizing there are 12x12=144 in2 to 1 ft2 without having to convert each term in the calculation. But since you've already converted the length ... note: if that is a diameter, the formula for the area is ##A=\pi d^2/4##

    Did you have a question?
  4. Nov 22, 2014 #3
    so i change the first part to Feet is 28+(4/12)=28.333 are the second and third parts correct ? if not please show me what i did wrong. thanks
  5. Nov 22, 2014 #4

    Simon Bridge

    User Avatar
    Science Advisor
    Homework Helper

    How many significant figures do you keep when you round off?
    Is the figure 28'4" a diameter or a radius?
  6. Nov 22, 2014 #5
    the assignment had some info I didnt post sorry. there were 4 different steps and i did them all right except for step one which is the one i posted


    To calculate the volume of a 28’4” diameter tank.


    The tank is 28’4” in diameter and 20 feet tall (bottom seam to top of side or roof seam). It should not be filled past 95% of its height. It holds benzene, which has a specific gravity of 0.84.
  7. Nov 22, 2014 #6
    ok i think i got it


    Converting to inches D=12feet * 12inches/foot +4 inches =340

    Converting to feet 28+(4/12)=28.333

    Radius r=d/2=340inches/2=170inches Or 28.333/2=14.167feet

    Area of the bottom in ft2 (square feet) = 3.1416*28.333 feet2 =2521947 feet2
  8. Nov 22, 2014 #7

    Simon Bridge

    User Avatar
    Science Advisor
    Homework Helper

    ... what does "D stand for?
    Where did you get that number from?

    ... taking "feet2" to mean "square feet"... then that would be the area of the tank.
    I guess my question about radius or diameter has been answered above. What about the other questions?
    Also: are you supposed to find the volume of the whole tank of just the maximum volume of benzine that it may contain?

    It is best practice to express the equations in terms of the data you have rather than convert the data into something the equation uses; so:
    The area of a circle, in terms of the diameter, is: ##A=\frac{1}{4}\pi d^2##
    It is OK to represent a dimension by a fraction - so the diameter would be (84/3)feet and the radius (42/3)feet.
    It is also OK to quote a volume in cubic-inches.
  9. Nov 22, 2014 #8


    Staff: Mentor

    I think Jim made a typo. D in the quoted text above is diameter, and he inadvertently wrote 12 when he meant 28.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted