• Happy 20 YEARS to us!

Physics - Got Some Questions (1 Viewer)

Life'sHard

Well-Known Member
Joined
May 24, 2021
Messages
879
Gender
Male
HSC
2021
1)
Screen Shot 2021-08-04 at 12.05.05 pm.png

Screen Shot 2021-08-04 at 12.05.17 pm.png
Little confused about the worked solutions, can someone show their working? Thanks!
 

Life'sHard

Well-Known Member
Joined
May 24, 2021
Messages
879
Gender
Male
HSC
2021
Here's how I would approach this - more of an algebra q. Sorry if i'm completely wrong haha
You are correct.
Screen Shot 2021-08-04 at 1.05.13 pm.png
Here's the sample answer provided. Can someone explain why 1.5*10^11 and not 1.5*10^8?

For part b) I've just realised I made a silly mistake tyvm.
 

Life'sHard

Well-Known Member
Joined
May 24, 2021
Messages
879
Gender
Male
HSC
2021
1)
Screen Shot 2021-08-04 at 4.56.23 pm.png

2)
Screen Shot 2021-08-04 at 4.57.21 pm.png

Fairly simple questions, but can someone please reason out the answers

3)
Screen Shot 2021-08-04 at 5.24.54 pm.png

4)
Screen Shot 2021-08-04 at 9.51.44 pm.png
 
Last edited:

CM_Tutor

Moderator
Moderator
Joined
Mar 11, 2004
Messages
2,766
Gender
Male
HSC
N/A
@Life'sHard, I haven't studied physics beyond first year uni level, and that was some while ago. However, I am a scientist and know the basics. For example, in this thread, I knew the Kepler's third law result (though I didn't recall the exact formula) and knew why it called for SI units. I recognise the others but am not certain enough to give any definitive answer. In short, I'll comment if I have something I see as helpful to add, but I won't routinely comment on physics questions.
 

CM_Tutor

Moderator
Moderator
Joined
Mar 11, 2004
Messages
2,766
Gender
Male
HSC
N/A
But, since you asked, here are my thoughts...

Someone, anyone, please correct anything that is wrong.

I think 1 is C because the laminations need to be parallel to the magnetic field induced by the coil to suppress the eddy currents and minimise heating.

2, I think might be C. Time dilation under special relativity is in play here, 0.9c being more than enough speed for dilation to be significant. However, I think this is asking about reciprocity, where both the cook and the cabin boy each perceiving themselves to be stationary and the other to be moving and thus each seeing the other as slowed due to time dilation, thus each seeing the same time taken.

With 3, the only acceleration is gravity assuming the ball is moving at a constant 1.1 m/s and that the table is frictionless. However, only the component of gravity in the plane of the table is acting as the component perpendicular to the table is cancelled by the normal force... so, I'm thinking .

As for 4, both objects have the same change in height and so convert the same amount of gravitational potential energy into kinetic energy (ignoring energy lost as heat due to friction in moving through the atmosphere). Crudely, this situation is
suggesting the same impact speed (I say crudely as is not constant if starting sufficiently far above the surface of the Earth). However, is moving in a decaying orbit and so starts with some speed and momentum whereas is initially stationary. Thus, has greater energy / momentum at impact than does , and so should have a greater impact velocity.

These are my thoughts based on recollections but may not be correct.
 

Life'sHard

Well-Known Member
Joined
May 24, 2021
Messages
879
Gender
Male
HSC
2021
@Life'sHard, I haven't studied physics beyond first year uni level, and that was some while ago. However, I am a scientist and know the basics. For example, in this thread, I knew the Kepler's third law result (though I didn't recall the exact formula) and knew why it called for SI units. I recognise the others but am not certain enough to give any definitive answer. In short, I'll comment if I have something I see as helpful to add, but I won't routinely comment on physics questions.
Thanks! All correct I'm pretty sure. We need some physics mods hahahaha.
 

notme123

Well-Known Member
Joined
Apr 14, 2020
Messages
878
Gender
Male
HSC
2021
But, since you asked, here are my thoughts...

Someone, anyone, please correct anything that is wrong.

I think 1 is C because the laminations need to be parallel to the magnetic field induced by the coil to suppress the eddy currents and minimise heating.

2, I think might be C. Time dilation under special relativity is in play here, 0.9c being more than enough speed for dilation to be significant. However, I think this is asking about reciprocity, where both the cook and the cabin boy each perceiving themselves to be stationary and the other to be moving and thus each seeing the other as slowed due to time dilation, thus each seeing the same time taken.

With 3, the only acceleration is gravity assuming the ball is moving at a constant 1.1 m/s and that the table is frictionless. However, only the component of gravity in the plane of the table is acting as the component perpendicular to the table is cancelled by the normal force... so, I'm thinking .

As for 4, both objects have the same change in height and so convert the same amount of gravitational potential energy into kinetic energy (ignoring energy lost as heat due to friction in moving through the atmosphere). Crudely, this situation is
suggesting the same impact speed (I say crudely as is not constant if starting sufficiently far above the surface of the Earth). However, is moving in a decaying orbit and so starts with some speed and momentum whereas is initially stationary. Thus, has greater energy / momentum at impact than does , and so should have a greater impact velocity.

These are my thoughts based on recollections but may not be correct.
I got the same for all the others and a very similar answer to 3. Strangely I got and for small values of : so I think it checks out.
 

notme123

Well-Known Member
Joined
Apr 14, 2020
Messages
878
Gender
Male
HSC
2021
I cant remember which past paper, I think CSSA or maybe ruse?
Out of the two, seems like CSSA to me because it has similar font to the 2019 one. I assume this is the 2020 one because the 2019 one didn't have good qs nor were the solutions correct.
 

CM_Tutor

Moderator
Moderator
Joined
Mar 11, 2004
Messages
2,766
Gender
Male
HSC
N/A
NSGHS has some really good questions in its maths exams so I am not surprised that the same is true of their physics exams. Definitely a source worth trying.
 

Users Who Are Viewing This Thread (Users: 0, Guests: 1)

Top