Wednesday

July 23, 2014

July 23, 2014

Posted by **Anonymous** on Wednesday, September 12, 2012 at 1:00pm.

Gold has a density of 19.3 g/cm3. Do you think you could carry 2.40 cubic ft (rhetorical--don't answer)? How many pounds does 2.40 cubic feet of gold weigh? [453.6 g = 1 lb, 2.54 cm = 1 in, and 1 ft = 12 in.]

7.42e-2

A scientific oven is programmed to change temperature from 51.4 ºF to 207.4 ºF in 1.50 minute(s). Express the rate of change in degrees Celsius per second.

-1.16

A bug is observed to travel 72 cm in 7.5 seconds. What is the bug's speed in miles per hour?

.21

Thank you!

- Chem -
**DrBob222**, Wednesday, September 12, 2012 at 1:43pma isn't even close. Show your work and I'll find the error.

b is close but I obtained 1.7 or thereabouts.

c. 0.214 is the factor for cm/sec to mph. You still must multiply by cm/sec which is 72/7.5.

- Chem -
**L**, Wednesday, September 12, 2012 at 1:50pmthanks! all i did for a was change 2.4 by converting it in the manner they said, from feet to inches, inches to centimeters. same with 19.3. i changes it from grams to pounds.

- Chem -
**Steve**, Wednesday, September 12, 2012 at 1:57pmsomething tells me you divided instead uf multiplying somewhere. In problems like this, be sure to keep track of the units, so you cancel out the ones you don't want.

As for you answer of .00742 lbs, even a cursory sanity check would give a clue that it's bogus. Gold is heavy. Could you lift a cubic foot of it? I doubt it. So, on to the calculations. You want to convert ft^3 to lbs, knowing the various equivalents.

2.4 ft^3 * 12^3 in^3/ft^3 * 2.54^3cm^3/in^3 * 19.3g/cm^3 * 1lb/453.6g = 2892 lbs

- Chem -
**L**, Wednesday, September 12, 2012 at 2:02pmGreat! Thank you!

- Chem -
**Steve**, Wednesday, September 12, 2012 at 2:12pmHey, no problem. It was a real epiphany for me when I took physics, when I found out that units could be canceled just like numeric factors.

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