Weight

[Guest]

A piece of lead is 1 in. square and 1 ft. in length. The specific gravity (ratio of weight of substance to equal volume of water) of lead is 11.01. Determine weight of lead piece.

Water weighs 62.5 lbs. per cu. ft.

1 * 12 = 12 cu. in.

12 / 1728 = .0069 cu . ft. (volume of piece).

.0069 * 62.5 = .431 lbs. (equal volume of water).

.431 * 11.01 = 4.745 = 4.75 lbs.

Where am I correct ?

[Guest]

Water weighs 62.5 lbs. per cu. ft. .........This says lbs per cu.ft

1 * 12 = 12 cu. in. ..................why are you working in cu.ins....Try and work in cu.ft

[Guest]

0.0833 * 1 = .0833 cu ft. (volume of piece).

0.0833 * 62.5 = 5.208 lbs. (equal vol. of water).

5.208 * 11.01 = 57.25 lbs.

??

[Guest]

a piece of lead 1 in x 1 in x 12 inches is 1/144 part of a cu. ft

[Guest]

1 * 1 * 12 = 1/144 = 0.06944 cu. ft. (vol. of piece).

0.06944 * 62.5 = 4.34 lbs. (equal vol. of water).

4.34 * 11.01 = 47.78 = 48 lbs.

I don't know.

[Guest]

Error in calculation: 1/144 = 0.006944 instead of 0.06944

0.006944 * 62.5 = 0.434 lbs.

0.434 * 11.01 = 4.778 lbs.

If that is incorrect, I still don't know.

[Guest]

You should try to have a method to your calculation and follow a logical sequence....
Start at the beginning and work towards the end........

a piece of lead 1 in x 1 in x 12 inches is 1/144 part of a cu. ft .... because 1/12 x 1/12 x 1 = 1/144 working in feet.
Water weighs 62.5 lbs. per cu. ft.
The specific gravity of lead is 11.01 ..... so lead weighs 11.01 times water ..... so is 11.01 x 62.5 lbs per cu.ft
and our piece of lead must weigh a fraction of that ..... a 1/144 part of 1 cu. ft

All of the above info was got from reading the question .......all you have to do now is work it out.........

[Guest]

11.01 * 62.5 = 688.125 lbs. / cu. ft. (weight of lead).

1 / 144 = 0.00694 cu. ft. (vol. of lead piece).

688.125 * 0.00694 = 4.775 lbs.

Not sure.

[Guest]

Yes, thats it.......

11.01 x 62.5 / 144 = 4.77 lbs

and hopefully you have also gained a logical method to enable you to solve other similar problems

[Guest]

I did. Thanks.

One question:

" a piece of lead 1 in x 1 in x 12 inches is 1/144 part of a cu. ft " Why did you use that conversion ?

[Guest]

" a piece of lead 1 in x 1 in x 12 inches is 1/144 part of a cu. ft " Why did you use that conversion ?

No conversion, I was only making a statement of fact....... because you seemed to start working in inches and the weight conversion in the question was in lbs per cu.ft.

Also you stated...... 1 * 1 * 12 = 1/144 = 0.06944 cu. ft. (vol. of piece)........ which does not read correctly as a written statement.....

The piece of lead was 1 ins x 1 ins x 1 ft long which is 1/12 ft x 1/12 ft x 1 ft = 1/144 cu.ft = 0.06944 cu.ft .....statement now reads correctly.

[Guest]

Ok, thanks again.

[leesajohnson]

Yes, your solution is correct.

[Guest]

Thanks.