Can't Do This Scuba Math....A test for you

[Blackwood]

WOW.....what scuba gurus. That is just what I needed. I figured that #1 was 53lbs, but thought that was too simple. (you know, one of those trick questions....) Thanks all. I might be asking some of you for more help later. (Physics test coming up)

It still may be a "trick question."

53 pounds of lead will displace about 5 pounds of water (assuming the density of lead to be 11,340kg/m^3)... in other words, 53 pounds of lead is only -48 lbs of buoyancy.

(note... I didn't check my work... just ran through the math to arrive at 5 pounds one time on a calculator)

 

[The Kraken]

At this point it's a matter of weight, not displacement.
The lead is negatively buoyant and WEIGHS 53 pounds.
The gravitational pull upon the lead will be 53 pounds.

 

[redacted]

At this point it's a matter of weight, not displacement.
The lead is negatively buoyant and WEIGHS 53 pounds.
The gravitational pull upon the lead will be 53 pounds.

I'm pretty sure Blackwook is right on this one. With lead a little over 10 times the density of lead, 53 pounds of lead will displace a about 5 lb of water adding a little less than .1 cu ft to the total lift requirement.

I did not expect the wt. difference to be that much from the estimate ignoring the volume of the lead.

 

[Blackwood]

At this point it's a matter of weight, not displacement.
The lead is negatively buoyant and WEIGHS 53 pounds.
The gravitational pull upon the lead will be 53 pounds.

Yes... the gravitational pull will be 53 pounds, and the upwards push of the water on the lead will be 5 pounds.

The question asked for 50# of negative bouyancy, not 50 pounds of weight, so for the same reason you must consider the displacement of the 125 pound object, you must also consider the displacement of anything you attach to the object (e.g. lead).

 

[The Kraken]

Yes, you are right.

 

[kensuguro]

oh c'mon guys, beyond a certain point it's going to start sounding ridiculous.. You can only deep fry the problem so much.

 

[The Kraken]

"Houston, we have a problem . . . "

Trust me, 1 pound can make the difference between living and dying.

the K

 

[redacted]

oh c'mon guys, beyond a certain point it's going to start sounding ridiculous.. You can only deep fry the problem so much.

What liberal arts degree are you seeking?

 

[WileEDiver]

It still may be a "trick question."

53 pounds of lead will displace about 5 pounds of water (assuming the density of lead to be 11,340kg/m^3)... in other words, 53 pounds of lead is only -48 lbs of buoyancy.

(note... I didn't check my work... just ran through the math to arrive at 5 pounds one time on a calculator)

Wait a minute! The question clearly directs you to disregard the minimal positive bouyancy (of the lead).

 

[Blackwood]

Wait a minute! The question clearly directs you to disregard the minimal positive bouyancy (of the lead).

I don't consider 5# to be minimal

(even in the context of -50#).