John has won a competition and is allowed to choose between two golden balls as a prize which look and feel identical and weigh exactly the same. One is a hollow ball of pure gold and the other a worthless metal alloy, gold in colour and very similar to gold. There are no markings including hallmarks on the balls and John is in the middle of a large room with nothing around that can usefully assist him to check what the balls are made of. How can John ensure that he picks the pure gold ball without tapping or bouncing them?

Has this got a joke answer? ;)

As in all the old westerns;

 

Bite it!!

 

:D

 

Matty.

Yeah pure 24ct gold will be soft.

He could stand on them, hollow gold one will crush.

If one of MY balls was pure gold, I'd know about it.

Turn the rooms heating thermostat up to 1064C, which is where the gold will melt.

EASY

The answer is:

 

 

 

If you roll both of them along the floor the hollow real gold ball will travel further

Why?

Originally posted by james300

Why?

 

LOL:D

 

Good point!!

No point in asking Roy he won't know, he just copied the answer from one of his colleagues LMAO

I don't know! LOL its a physics thingy!!! So Stu, yes your right:D

Ask Nelson cos it will be more of a MASS thing ;)

No sorry - u said they weighed the same.

Easy the rotational energy in the hollow ball will also be highter than the rotational energy of the solid since more of the mass will be rotating faster.

Originally posted by Zimon

Easy the rotational energy in the hollow ball will also be highter than the rotational energy of the solid since more of the mass will be rotating faster.

 

I was just about to say that!:D

Pressuably, it IS something to do with the mass - however, mass DISTRIBUTION is the key. Because the gold ball has all of its mass at the perimeter of the ball, it will have more rolling inertia than the solid ball.

 

Make sense?

Originally posted by andyduff

Pressuably, it IS something to do with the mass - however, mass DISTRIBUTION is the key. Because the gold ball has all of its mass at the perimeter of the ball, it will have more rolling inertia than the solid ball.

 

Make sense?

 

Some people are so slow:D

How do you ensure you roll them with the same energy imposed?

Originally posted by andyduff

.. Because the gold ball has all of its mass at the perimeter of the ball, it will have more rolling inertia than the solid ball...

Correct so it takes more Force to Accelerate the hollow ball to the same rotational speed as the solid one. If the same Force was applied to both then they would have different rotational speeds BUT the same amount of rotational energy!

Originally posted by The Devil

How do you ensure you roll them with the same energy imposed?

As above ... the key here is to make them start of with the same rotational speed thus due to its higher moment of inertia the hollow ball has to have more energy although they are going at the same speed!

This seems strange as you would have thought that their kinetic energies are the same weirdly this is true their linear kinetic energies are the same but their Rotational kinetic energies are not! As I said weird!!

Id just stand on them

I'd question the sexuality of anyone who makes this shit up!:D