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Author Topic: Harder Physics Questions  (Read 8352 times)  Share 

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Edmund

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Re: Harder Physics Questions
« Reply #90 on: March 07, 2010, 11:04:29 pm »
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Aah thanks, I calculated the density with the timber floating horizontally =/
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Edmund

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Re: Harder Physics Questions
« Reply #91 on: March 20, 2010, 09:07:51 pm »
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GAMSAT over! Came across some interesting questions I might like to share :P

For 1 mark (1.5 minutes),

The amount of energy needed to raise 1 mL of water by 1C is 4.2 J. One meal served in a restaurant is equivalent to 8000 kJ. If all the energy is converted to heat, how much ice water with a temperature of 0C must a diner (body temperature =37C) drink to maintain his body temperature (or counteract this increase in energy input)?

Feel free to clarify since I might not remember the question too well.

The options were 50L, ~70L, cant remember the other two options though... ;)
2007-2008 VCE ATAR 90.15
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appianway

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Re: Harder Physics Questions
« Reply #92 on: March 20, 2010, 09:16:04 pm »
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Energy that the water gains = energy converted to heat.

Energy that water gains = volume of water * change in temperature * 4.2J
Change in temperature = 37 degrees

37 * 4.2 * V = 8 * 10^6
V = 8* 10^6 / (37*4.2)

And yeah, just plug it in.

Edmund

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Re: Harder Physics Questions
« Reply #93 on: March 20, 2010, 09:20:20 pm »
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Well that looks right, I probably forgot the formula and guessed it wrong
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iamdan08

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Re: Harder Physics Questions
« Reply #94 on: March 20, 2010, 10:12:10 pm »
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From memory, I'm pretty sure i got 50L. Can't remember the exact question though. :S
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Re: Harder Physics Questions
« Reply #95 on: May 07, 2010, 01:33:17 pm »
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A nice problem back from my first quantum problem set:

Show that, if a photon collides with a stationary electron, they cannot both emerge
from the collision along the same trajectory.

Useful Formulae:
Relativistic momentum:
Rest energy:
Relativistic total energy:
Photon Energy:

Where

Hint: Reductio ad Absurdum


(I'll post up a really good question after I hand in my current thermo assignment xD)
« Last Edit: May 07, 2010, 01:49:31 pm by /0 »

schnappy

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Re: Harder Physics Questions
« Reply #96 on: May 10, 2010, 08:22:36 pm »
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GAMSAT over! Came across some interesting questions I might like to share :P

For 1 mark (1.5 minutes),

The amount of energy needed to raise 1 mL of water by 1C is 4.2 J. One meal served in a restaurant is equivalent to 8000 kJ. If all the energy is converted to heat, how much ice water with a temperature of 0C must a diner (body temperature =37C) drink to maintain his body temperature (or counteract this increase in energy input)?

Feel free to clarify since I might not remember the question too well.

The options were 50L, ~70L, cant remember the other two options though... ;)

Trick question the water is in a solid state so it can't be readily consumed :P :P :P :P

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Re: Harder Physics Questions
« Reply #97 on: May 11, 2010, 07:13:00 pm »
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How long do black holes last?

1) The Schwarzchild radius of a Black Hole is the radius of the 'event horizon', past which even light cannot escape.
Find an expression for the Schwarzchild radius of a black hole using the notion of escape velocity (non-rigorous derivation :-o)

2) Over time, black holes lose energy and hence mass via "Hawking Radiation". The power emitted by a Black hole is:
, where , and is Planck's constant, is Boltzmann's constant, and is the speed of light, is the surface area, is emissivity, and is temperature.
Since we may assume a black hole to be a perfect blackbody (perfectly absorbs and emits radiation), .
Given that the temperature of a black hole is: , where is the Gravitational constant, and the energy of a black hole is , form a differential equation to find the lifetime of a black hole in terms of its initial mass.

3) How long would a black hole the mass of the sun last ()? How about the mass of a proton ()?
« Last Edit: May 11, 2010, 07:50:37 pm by /0 »