Physics question from DM exam

[LowVizWiz]

Don't be ridiculous. The object is positively buoyant. It has no chance of falling to the bottom.

Shessh - some people.

Not after adding 53# or is it 50???

Okay let's call it 51.5! still is sinking rapidly so does it make a sound?

 

[NudeDiver]

To add 50lbs of negative buoyancy to something that is already positive, first you have to overcome the amount which the object is positive -- thus, in this case, you need to add 53lbs of lead to add 50lbs of negative buoyancy.

Dude, that's just not correct!! Consider:

To add -50 to something that is already +3, first you have to overcome the +3 -- thus, in this case, you need to add -53 to add -50.

Does that seem like a correct statement to you????

Again - basic math: +3 + -50 = -47 However, you still ADDED -50!!!

 

[NudeDiver]

so does it make a sound?

Depends on what it hits. If it hits a silly diver who can't do basic math involving negative numbers, then probably not.

 

[Gombessa]

To add 50lbs of negative buoyancy to something that is already positive, first you have to overcome the amount which the object is positive -- thus, in this case, you need to add 53lbs of lead to add 50lbs of negative buoyancy.

That's the major problem I have with that interpretation of the literal wording of the question.

In order to "add 50# of negative buoyancy" to an object that is positively buoyant, you're arguing that you have to first add an amount of weight to cancel out the positive buoyancy of the object, and then add 50# to that to achieve "a total of" 50# negative.

That definition breaks down if the object is already negative. If it's negative by an amount less than or equal to 50#, then you're never "adding 50# of negative buoyancy" to it by making it equal -50# bouyancy, you're literally "adding (50 - (original negative buoyancy)# to it to make it equal -50# total." The problem there is that is not what the question asks.

However, if you then change the meaning to account for this by merely adding -50# to the object, the answer for any negatively buoyant object would always be "50lb" no matter how negatively buoyant it started at, whereas you would refuse to accept that same answer if the object were positive to begin with.

Gawd that was convoluted.

 

[SparticleBrane]

Depends on what it hits. If it hits a silly diver who can't do basic math involving negative numbers, then probably not.

I suppose it all depends on the wording...

I can assure you, I can do basic math. :cool2:

 

[NudeDiver]

Johnny has 3 apples. If you beat the **** out of Johnny and take away 50 of his apples, how many of his apples have you taken away?

The answer is 50. Not 53.

 

[SparticleBrane]

Johnny has 3 apples. If you beat the **** out of Johnny and take away 50 of his apples, how many of his apples have you taken away?

The answer is 50. Not 53.

 

[NudeDiver]

I suppose it all depends on the wording...

The wording is provided in the question. What is the answer based on the wording provided? 50.

 

[Gombessa]

I suppose it all depends on the wording...

I can assure you, I can do basic math. :cool2:

I agree with both statements above. Happily, this is a question where both sides have a legitimate claim to victory.

I would have answered 50# and contested it with the instructor to make a point (yeah, that's a jerk thing to do).

It's like when a 3rd grade teacher asks the class "Who discovered the new world?" Yeah, I know you want me to say Columbus, but it's wrong and I'm not gonna do it.

 

[NudeDiver]

little Johnny is also carrying a sack that contains a dimensional vortex that leads to an Apple orchard. Even though he is only carrying 3 Apples (well, he was until you beat the **** out of him), you can access additional Apples via the dimensional vortex he is carrying.

Were I going to beat the **** out of him, I would have let him keep his 3 Apples and just steal the sack containing the dimensional vortex. But not you. Oh no! You just wanted the Apples. Must be some kind of fruit lover I guess.