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physics help

hiya,
my sister is doing her physics hw and is struggling with a couple of questions and asked me to post them on here to see if anyone could push her in the right direction to answer them. thanks!

12.1)
the diameter of a tennis ball is 66mm. how many tennis balls will it take to fill a box with sides of 1m if they are all stacked together with a cubic structure?

12.6)
a copper connecting wire has a cross sectional area of 3mm2 and is 30cm long. estimate the amount of free charge in this wire. how long will it take for all this free charge to pass through the wire when a current of 3A flows? hence find the av. speed at which this free charge moves.

12.7)
explain why your room light comes on at almost the same instant as you close its switch despite the very slow movement of the electrons in the wires connecting it to the mains supply.

12.11)
a copper wire, as used for house mains wiring, has a cross sectional area of 2.5mm2 and carries a max current of 25A. the charge is carried by electrons, of which there are about 7.0 x 10^28 per metre cubed. the charge on an electron is (-) 1.6 x 10^-19 C. calculate the drift speed of the electrons when the wire carries its max current.
for this, i think she can use i=naqv, am i correct?

12.16)
describe how you would demonstrate the slow speed at which the current carriers move through a circuit.


thank you very much in advance
12.1)
the diameter of a tennis ball is 66mm. how many tennis balls will it take to fill a box with sides of 1m if they are all stacked together with a cubic structure?
make 66mm into metres so it would be 0.066 i believe. a box is cubical i assume, therefore how many 0.066 go into 1?

the others im too lazy to answer, sum1 else will prolly do it for u lol...
Reply 2
Avatar for tillhm
tillhm
coolduck

12.1)
the diameter of a tennis ball is 66mm. how many tennis balls will it take to fill a box with sides of 1m if they are all stacked together with a cubic structure?


I doubt you are going to be able to give one answer for this question. There are two possibilities
(1) The diameter (or edge length) of the ball remains constant => The volume increases.
(2) The volume remains constant => The edge length decreases.
tillhm
I doubt you are going to be able to give one answer for this question. There are two possibilities
(1) The diameter (or edge length) of the ball remains constant => The volume increases.
(2) The volume remains constant => The edge length decreases.


Tennis balls don't have edges - they have surfaces.

You can get 3375 balls of diameter 66mm into a 1m cube, packed as stated. The answer would be different if they are in interlocking layers.
Reply 4
Avatar for tillhm
tillhm
Good bloke
Tennis balls don't have edges - they have surfaces.

You can get 3375 balls of diameter 66mm into a 1m cube, packed as stated. The answer would be different if they are in interlocking layers.


Yep, I confused "cubic structure" with "balls being pressed into a cubic form" :redface:

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