VCE Physics Question Thread!

[lzxnl]

1. Explain the importance of keeping a lid on a simmering saucepan of water in terms of latent heat of vapoiurisation?

2. Explain in terms of the kinetic particle model why you can put your hand safely in a 300C oven for a few seconds, while if you touch a metal tray in the same oven your hand will be burned

3. How does evapouration of water cause a reduction i the temperature of the surrounding air?

I am findinng Physics very difficult and my teacher just reads from the textbook, so it would be nice if anyone can provide an answer and explain it in detail so i can understand it thank you!

1. Assuming you want to boil the water, if you keep the water exposed to the atmosphere, then the water's rate of heating will drop a lot due to heat exchange with the cooler atmosphere (heat flows from hot to cold, remember). The issue is, you need to input a certain amount of energy into the water (latent heat of vapourisation) for the water to evaporate, so your task is made doubly hard if you don't keep a lid on.

2. The kinetic particle model suggests that temperature is a measure of the average kinetic energy of particles. Now, for your hand to get hurt in that oven, the gas particles in the oven have to collide with your hand and impart enough energy to heat your hand. The problem is, gas particles aren't very concentrated, so the energy transfer won't be very fast. In contrast, particles are a lot more concentrated in a metal, so there will be a LOT more particle collisions if you touch a hot metal tray to heat your hand and the heat transfer will be much faster.

3. Evaporation of water requires absorbing energy from the surroundings. To conserve energy, this energy must come from the atmosphere, which will consequently decrease its temperature as its energy drops.

[Ramones]

How does strong and weak interaction work?

[Syndicate]

Hey guys,

Just a question about special relativity: Why does time appear to be "slower" for the object in motion relative to the observer, which is technically (not exactly) stationary. I know that a longer distance is being travelled, by lets say a light beam, due to it's horizontal speed (which means it takes a longer amount of time). Shouldn't the time be passing faster, in order to reach it's destination in the same time interval as the clock (where one tick = the light beam travelling back and forth) held by the observer which we are assuming stationary in this case. I don't really know why the time get slower as we approach c. Can someone explain this in terms of words? I know how it works using the formula, but don't really understand the concept that well.

Thanks   

[-273.15]

Hey guys,
Im stuck with questions where there are objects in a system
e.g. trailer and truck and have to find acceleration, tension, with and without friction

could someone please give me some tips / rules for working out these questions / any helpful info???
thanks heaps

[Shadowxo]

Hey guys,
Im stuck with questions where there are objects in a system
e.g. trailer and truck and have to find acceleration, tension, with and without friction

could someone please give me some tips / rules for working out these questions / any helpful info???
thanks heaps

Often the easiest way is to consider it as a whole system. eg if the truck is pulling the trailer with a force of 2000N and their combined weight is 1000kg, F=ma => a = 2ms^-2 ignoring friction. If not ignoring friction, you have to use the net force. If the friction on each of the truck and trailer is 250N, F net= (2000-250-250)=ma
Then if you want to find the tension of the connection between the truck and trailer, use F=ma again, where a= 2ms^-2 (from earlier) and the mass of the trailer only, eg 250kg. F=ma = 500N. If not ignoring friction, F net = 500 = F (from truck) - friction   => F from truck = 750N
Often drawing diagrams can help a lot too.

Often questions are similar to that. If you get stuck on a specific question I can answer in a bit more detail
Hope this helps

[-273.15]

Often the easiest way is to consider it as a whole system. eg if the truck is pulling the trailer with a force of 2000N and their combined weight is 1000kg, F=ma => a = 2ms^-2 ignoring friction. If not ignoring friction, you have to use the net force. If the friction on each of the truck and trailer is 250N, F net= (2000-250-250)=ma
Then if you want to find the tension of the connection between the truck and trailer, use F=ma again, where a= 2ms^-2 (from earlier) and the mass of the trailer only, eg 250kg. F=ma = 500N. If not ignoring friction, F net = 500 = F (from truck) - friction   => F from truck = 750N
Often drawing diagrams can help a lot too.

Often questions are similar to that. If you get stuck on a specific question I can answer in a bit more detail
Hope this helps

Thank you so much this helped a lot

[dylang99]

Hi All,

Any help would be much appreciated:

A high-energy physicist detects a particle in a particle accelerator that has a half-life of 20 s when travelling at 0.99c.
(a) Calculate the particle’s half-life in its rest frame.


Thank you in advance

[Syndicate]

Hi All,

Any help would be much appreciated:

A high-energy physicist detects a particle in a particle accelerator that has a half-life of 20 s when travelling at 0.99c.
(a) Calculate the particle’s half-life in its rest frame.


Thank you in advance

L= 20
L0 = ?
v= 0.99c

L= L0Y
20 = L0 x 7.089

L0 = 2.82 seconds

[Mattjbr2]

Hi guys,
Is this merely a rounding error in my calculations? The worked solutions are clearly wrong, so I can't rely on them.
I don't know what I'm missing in this question.
Note that the question says 20 degrees to the vertical, which means 70 degrees to the horizontal. So I used 70 in my calculations.
The book says 78.9kg.

Edit: The book used 10ms^-2 for g. So my method is correct. Never mind! 

[sweetiepi]

Hi guys,
Is this merely a rounding error in my calculations? The worked solutions are clearly wrong, so I can't rely on them.
I don't know what I'm missing in this question.
Note that the question says 20 degrees to the vertical, which means 70 degrees to the horizontal. So I used 70 in my calculations.
The book says 78.9kg.

I got 80.92kg as my answer, without rounding, however, I tried again with g=10 and got 78.9.
Therefore you are correct, as the new study design dictates that g=9.8, not g=10

Hope this helps!

[Mattjbr2]

I got 80.92kg as my answer, without rounding, however, I tried again with g=10 and got 78.9.
Therefore you are correct, as the new study design dictates that g=9.8, not g=10

Hope this helps!

Cheers 

[Gogo14]

How do you do q8,9
Thanks

[vcestressed]

Is it only 'electricity' and 'motion' that is assumed knowledge from unit 1 & 2 for physics 3 & 4 for the new study design? Would appreciate if someone could clear this up for me. Thanks

[Syndicate]

Is it only 'electricity' and 'motion' that is assumed knowledge from unit 1 & 2 for physics 3 & 4 for the new study design? Would appreciate if someone could clear this up for me. Thanks

Yep. Basically everything from 1D motion, which is then used to extend upon 2D physics (projectile motion, circular motion, special relativity (not sure if I should have included that here)). For electricity, I found that half of the content covered in units 1/2 is unnecessary (we go over different stuff, however, the formulas are still used).

[vcestressed]

Yep. Basically everything from 1D motion, which is then used to extend upon 2D physics (projectile motion, circular motion, special relativity (not sure if I should have included that here)). For electricity, I found that half of the content covered in units 1/2 is unnecessary (we go over different stuff, however, the formulas are still used).

Thank you!