Middle School Math Problem?

Question

A representative column has diameter 42 inches, height 40 feet, and weight 15 tons. What is the mean number of pounds per cubic foot? Round your answer to the nearest whole number.

I have no idea how to get the answer. >_<

Answer 1

pounds / ft^3 .. needs volume

V(cyl)= pi r^2 h

(3.14)(1.75)^2 (40) = 384.8451001

15*2000 = 30,000 lbs

30,000 / 384.8451001  = 77.9534

78 lbs / ft^3

Answer 2

V=pi(r^2)(h)=3.14(3.5^2)(40) (42 in.=3.5 ft, always be consistant!) = about 1539 cubic feet.

D=m/v=30000/1539= 19.49=19 lbs/ft^3

Answer 3

For volume I get 384.8 cubic feet

For weight (converting tons to lbs) I get  33069 lbs

So, for average (mean) density I get 33069/384.8 = 85.9 lbs/cu. ft.

At this density &#039;they aren&#039;t stone or concrete&#039;

Answer 4

First find the volume. V = πr^2 * h or π(d/2)^2 * h

Density (lbs/cf) = V / lbs or V / (tons * 2000)

Even if you aren&#039;t familiar with density, you can figure it out just by looking at the units used. You know that you need lbs/cf, so you&#039;re dividing weight by volume. If you need mi / hr, you&#039;re dividing distance by time.

Answer 5

diameter 42 inches = (42/12) ft = (7/2) ft,

volume of column = pi D^2H/4 = (22/7)(7/2)^2(40)/4 ft^3

weight = 15 tons = 15*2240 lbs

number of lbs per ft^3 = 15*2240 / (22/7)(7/2)^2(40)/4 = 87 3/11 lbs/ft^3

rounded 88 lbs per cubic foot.