HSC Physics Question Thread

[arunasva]

Thanks.

I've got another question: In the topic of escape velocity, why does the object have 0 velocity and 0 energy at infinity?

With Gravitational Potential energy, the value of the energy itself at a point is not relevant as it does not give you any important information. But... the difference in energy after something went from one point to another is. So if you take the potential energy as 0 on the surface of the earth (mgh) or take 0 a  10^5km from earth it does not matter. You can define the 0 point yourself. Since gravitational fields only exert 0 force at infinity GPE is considered 0 at infinity. As for velocity even Idk 

[Shadowxo]

Thanks.

I've got another question: In the topic of escape velocity, why does the object have 0 velocity and 0 energy at infinity?

Just to elaborate on arunasva's post,

The escape velocity is the minimum velocity required to escape the planet's gravitational field. So, at infinity, all the kinetic energy has been used up to get away from the gravitational field / has been converted into grav potential energy, so velocity and k.e. are 0. And at infinity, gravitational potential energy is zero (as at an infinite distance, you don't feel the effects of it). Note that all the kinetic energy was converted into grav potential energy, so the grav potential energy increased up to 0, as gpe is negative.
Hence, at infinity, both velocity and energy are zero.

If the velocity were greater than the escape velocity however, this would not be the case as at infinity both velocity and k.e. would be positive.

[arunasva]

Just to elaborate on arunasva's post,

The escape velocity is the minimum velocity required to escape the planet's gravitational field. So, at infinity, all the kinetic energy has been used up to get away from the gravitational field / has been converted into grav potential energy, so velocity and k.e. are 0. And at infinity, gravitational potential energy is zero (as at an infinite distance, you don't feel the effects of it). Note that all the kinetic energy was converted into grav potential energy, so the grav potential energy increased up to 0, as gpe is negative.
Hence, at infinity, both velocity and energy are zero.

If the velocity were greater than the escape velocity however, this would not be the case as at infinity both velocity and k.e. would be positive.

ohhh thanks

[austv99]

Might be a rookie question but  some clarification for this question is appreciated -part ii

TIA

[katnisschung]

what is the speed for matter waves?

I got this rather simple question wrong when revising content (probably becos i don't know quanta to quarks well enough)
calculate the frequency of the matter wave when a neutron is made to move at 53.6x10^3 m/s
so why is it that they take 'c' as the speed. do all matter waves travel at c

[arunasva]

Might be a rookie question but  some clarification for this question is appreciated -part ii

TIA

From my chemistry knowledge, I'm guessing cos the first reaction releases a neutron, so that neutron can bombard  atoms to bring about the reaction. In the subsequent fission more neutrons are produced these have the capacity of bombarding even more atoms to bring about fusion and it goes on and on the next fission will  produce more neutrons than the previous one which will keep bombarding atoms to release energy. That's why power plants have an absorber thingy to absorb neutrons and control the rate

[austv99]

Help is appreciated for 14, 18, 19.
All from 2015 HSC

[blasonduo]

Help is appreciated for 14, 18, 19.
All from 2015 HSC

Hello! I hope I can explain this well

14) For these questions especially, I'd like to picture myself in these situations and go from there. Imagine you are driving a car, speeding it up or slowing it down will NOT make you experience a force to the left or right (there is no circular motion!), so this eliminates both B and D. Now referring back to the car analogy, when you turn the car, you'd always experience a force opposite to the way you are turning. The car is beginning its turning motion while you continue in a straight line path. This is because of Newton's first law.

So back to the question, the ball began to roll down the page, and from what was said before, it must mean the train was turning up the page, or to the RIGHT, so it is C.


18) For this, a bit of calculation is best for the description.

Let's assume a couple things for the equation






 





19) This is MUCH easier if we rule out the incorrect ones, For A, the force of gravity is NOT negligible, as that's what keeps objects in orbit! so it is wrong. While B is true, this is not answering the question, it is just a statement.

We now have it to C or D, for C, IF the forces were to be the same, (ie F = ma) since, the question claims F is the same, while mass is different, their accelerations must be different, and well, if their accelerations are  different, how on earth can they travel at the same speed? So C is incorrect, leaving only D as the answer (if you would like me to explain why, i'll be happy to!)


I hope this helps!

[bsdfjnlkasn]

Hey there!

I just have a few questions from the Quanta to Quarks option module and was hoping to get some help

1. What was it about Thomson’s model that led Rutherford to believe no large angle deflections would occur?


2. Where did the nitrogen atoms come from in Chadwick’s experiment? The following dot point was in a summary I found online and it's just really confusing to me. It's for the dot point which asks how Chadwick used conservation laws to discover the neutron. I get nuclei of hydrogen atoms because that's simply referring to the protons that were dislodged from the paraffin wax as a result of the neutron's colliding with them. But Nitrogen? It's a mystery to me.
•   Chadwick measured the recoil of the nuclei of hydrogen and nitrogen atoms after interacting with the natural radiation.

3. Do we need to know the details of the specific violations which led Pauli to propose the existence of neutrino? There are two conservation violations that i've read up on, but I don't know how relevant the actual details are. Here is the paragraph that specifies these:

•   During beta decay, initially scientists thought only beta particles were emitted. When they evaluated the energies involved, they came up with a figure for the maximum kinetic energy that a beta particle should have. All beta particles should have been emitted with this velocity, but this wasn’t the case. Instead, almost none were emitted with the full amount of kinetic energy, and most of them were emitted with significantly less. This meant that the slow beta particles were missing kinetic energy, leading to a violation of conservation of energy. Also, the sum of the momentums before and after beta decay was not equal - assuming the nucleus starts off stationary, the sum of momentums should be zero. However, when the momentums of the beta particle and the remainder of the nucleus were added, it was not zero, so conservation of momentum was being violated.

Thank you so much!!

[Sukakadonkadonk]

Hi,
I have a quick question, could you say that the magnitude of torque increases as motor speed increases (of course, regarding a motor)?

Thanks.

[winstondarmawan]

18) For this, a bit of calculation is best for the description.

Let's assume a couple things for the equation






 




I hope this helps!

Don't galvanometers measure current?

[bsdfjnlkasn]

Hi,
I have a quick question, could you say that the magnitude of torque increases as motor speed increases (of course, regarding a motor)?

Thanks.

Hey! If we look at the formula for torque: t =  nBIA cos(a) we can deduce that torque is only affected (considering they are proportional) by:
1. The number of turns on the coil
2. Strength of the magnetic field
3. The size of the current travelling through the coil
4. Area of the solenoid (multiply the side lengths of the coil)
5. Angle between the plane of the coil and the magnetic field


Because of this, the speed won't affect the torque acting on the coil as a result of the magnetic field in which it's in

[bsdfjnlkasn]

Might be a rookie question but  some clarification for this question is appreciated -part ii

TIA

Hey, i'll give this a shot

Energy is released as a part of radioactive decay as it assists in stabilising the radioactive nucleus. This is also explained by the fact that new elements are being formed (i.e. nuclear transmutation).

[Sukakadonkadonk]

Hey! If we look at the formula for torque: t =  nBIA cos(a) we can deduce that torque is only affected (considering they are proportional) by:
1. The number of turns on the coil
2. Strength of the magnetic field
3. The size of the current travelling through the coil
4. Area of the solenoid (multiply the side lengths of the coil)
5. Angle between the plane of the coil and the magnetic field


Because of this, the speed won't affect the torque acting on the coil as a result of the magnetic field in which it's in

Hey! Thanks for response.
I don't know, I just find it confusing because if I picture myself manually rotating a motor faster, it just seems like the torque would increase.
How do I wrap my head around this? Just remember the torque equation?

[bsdfjnlkasn]

Hey! Thanks for response.
I don't know, I just find it confusing because if I picture myself manually rotating a motor faster, it just seems like the torque would increase.
How do I wrap my head around this? Just remember the torque equation?

No worries

I think keeping in mind the formula is a good thing to do. Perhaps you're trying to link increasing the rate of rotation with the concept of magnetic flux. Because indeed, when you start to turn the coil faster, the rate of change in magnetic flux increases, and the more it increases, the greater the current that is induced. But other than that, torque is only dependent on the variables I listed above because torque is the turning effect of a force acting on an object. The speed will not change how the coil will turn in terms of the forces experienced

Let me know if you have anymore questions