MedVision ad

Physics Predictions/Thoughts (8 Viewers)

H

hughjanus_

New Member
Joined
Oct 19, 2023
Messages
7
Gender
Male
HSC
2024
For question 20 - if C is correct, wouldn’t that also imply that B is correct? Also, despite the fact that Z is travelling faster than X from an external frame of reference, from the inertial frame of reference of X, Z appears to be stationary. Wouldn’t this mean X and Z tick at the same speed?

Interested to hear everyone’s thoughts, as my cohort was quite sure it was B.
 
C

c4m3r0n

New Member
Joined
Jun 22, 2024
Messages
2
Gender
Male
HSC
2024
Does anyone know the solution to 29b? Different masses seems obvious but the question specifically states that mass is negligible.
 
U

uart

Member
Joined
Dec 10, 2008
Messages
69
Gender
Male
HSC
N/A
K1uggie said:
Why cant 20 be B
Click to expand...
hughjanus_ said:
For question 20 - if C is correct, wouldn’t that also imply that B is correct?
Click to expand...
That's a fair criticism, 20-B is certainly a correct statement. It just doesn't give as good a comparison of time dilatation effects for all three clocks as does 20-C. So 20-C will definitely be the accepted answer.


Also, despite the fact that Z is travelling faster than X from an external frame of reference, from the inertial frame of reference of X, Z appears to be stationary. Wouldn’t this mean X and Z tick at the same speed? Interested to hear everyone’s thoughts, as my cohort was quite sure it was B.
Click to expand...
That's taking the inertial reference frame approximation way too far unfortunately. The question says to "assume that the satellites are inertial ref frames" just so we know that it's valid to apply the usual SR time dilation formula. You can't entirely ignore the system rotation (like assuming the Earth is non rotating and that the GS satellite is just hovering up there in space) - Which is essentially what you're doing with that statement.
 
Last edited:
U

uart

Member
Joined
Dec 10, 2008
Messages
69
Gender
Male
HSC
N/A
asdlfkjhdsalf said:
What was the one with the uniform and radial gravitational fields
Click to expand...
Q31, compare the maximum height reached by a vertically launched projectile under the two different assumptions.

Assumption A - constant (uniform) gravitational field. g=9.8 m/s^2 and potential energy U = mgh.

Assumption B - (downward) gravitational acceleration is


and potential energy is


Qualitative answer.
g is just the point value of GM/r^2 at the Earth's surface (r = 6380x10^3 m), but an over estimate for higher elevations. This means that assumption A will generally under estimate the maximum elevation, as it over estimates the strength of the gravitational field at higher elevations.

Quantitative answer.
Equate changes in PE (U) to the initial KE, to obtain a formula for the max height under each assumption.

A :


B:


Not really sure how much of a quntatitve answer they will want here? The equation for B is a bit unwieldy, it can be algebraically simplified a little bit more, but still not easy to tell by cursory inspection that it's even an approximation to the equation of A (well technically A is an approx of B). If you sub in some numbers however then you'll see they are a close approximation. For u<100 m/s the maximum height reached will be very similar for both. At u>1000 m/s however, you'll notice some significant under estimates in equation A.
 
Last edited:
You must log in or register to reply here.

Users Who Are Viewing This Thread (Users: 0, Guests: 8)

Top