# Search results

1. ### 2022 Physics QAT MCQ Doubt

Sure fair enough but that was just an extreme example - I don't actually need a zero velocity for the argument to work. For instance, I could assume that she opens the parachute when she is falling downard at 0.01 m/s (i.e. something definitely below the terminal velocity). In that case, the...
2. ### 2022 Physics QAT MCQ Doubt

I don't think this is true in general. Suppose that they opened the parachute immediately when they jump (i.e. at zero downward velocity). Therefore in spite of the parachute being opened, their downward speed will still continue to increase because their weight force exceeds air resistance.
3. ### 2022 Physics QAT MCQ Doubt

I agree with someth1ng. I assumed in my response that when the question stated "terminal velocity" , it was the "terminal velocity" of the person + the parachute.
4. ### MCQ help

I think the answer should be C (no change in frequency, speed decreases) The frequency of any wave never changes when it moves into a different medium. This is because the frequency is dependent only on the source of the wave. Another way of seeing this is that if the photon frequency changes...
5. ### 2022 Physics QAT MCQ Doubt

I think the answer should be B (downward acceleration, downward speed) - please see my reasoning below (apologies for the lengthy explanation, but I think this question is a bit subtle / confusing so I spelled out my reasoning in detail). EDIT: Note that this explanation assumes that "terminal...
6. ### How does the W and Z Bosons contribute to the Strong nuclear force?

It doesnt. W and Z bosons mediate the weak force. The strong force is mediated by gluons.
7. ### how are these molecules the same?

Another way of seeing this is that you need to do 2 "swaps" to go from the molecule on the left to the molecule on the right. E.g. to go from the one on the left to the right you swap the H atom with the CH3 group and the C2H5 group with the OH group around the chiral carbon. if you need an...
8. ### Why do all acid base reactions especially strong acid and weak base go to completion

You can think about it iteratively. Supposed you had a weak base called "B-" which accepts a proton in this equilibrium. HB <-> B- + H+ Now what happens if you add an acid (i.e. HA) to the solution from a strong acid? Then whatever B- is availabile will accept the H+ and form HB to oppose...
9. ### inverse and compound angle qn

The question is wrong and doesn't make sense. sin-1(x) + cos-1(x) = pi/2 for all -1<=x<=+1. So it only makes sense for the case k = pi/2, and x can be anything in the domain of sin-1 & cos-1. (You can see that the LHS is constant by differentiating LHS and seeing that it equals zero.)
10. ### relation between stopping voltage and the work function - photoelectric effect

There is no direct relationship between the two - we also need to know the frequency of incident light. KE = hf - W \\ qV_s = hf - W \\ V_s = \frac{hf-W}{q} where V_s = stopping voltage, f = frequency, W = work function, q = electron charge.
11. ### Forces

At the top of the loop, there are two forces acting on the object: F_{Normal}, mg. The required centripetal force also points downward. Therefore F_{c} = F_{Normal} + mg \implies F_{c} - mg = F_{Normal} Note that we must have F_c - mg > 0 , otherwise the object is moving too slowly to...
12. ### Doppler vs pressure broadening?

I don't think this it is a meaningful question to ask how the two can be differentiated because in practice, when you look at absorption or emission spectrum it will be broadened due to multiple factors at the same time (i.e. the pressure broadening is layered on top of doppler broadening). You...
13. ### How to determine the direction of eddy current?

Another better way of figuring this out rather than to try use Lenz's Law is to imagine a test positive charge sitting on the metal disk and apply the Lorentz force law (F=qvB or F = IBL). The test positive charge is moving to the left when the disk rotates into the magnetic field (so I, the...
14. ### Doppler vs pressure broadening?

Doppler broadening is driven by the fact that the source of light is moving towards (blue shifting) or away (red shifting) from the observer. This can be due to random thermal motion or in the context of stellar spectra, the rotation of the source (i.e. if the star is rotating, one half rotates...
15. ### Can someone explain how to derive ac = v^2/r ?

The equation for centripetal accelaration is a kinematic one. It is a bit algebraically involved, so I'll point you to two sources 1. http://hyperphysics.phy-astr.gsu.edu/hbase/cf.html 2. https://physics.info/centripetal/ Note that since accelaration is a vector, there are two things that need...
16. ### Physics Degree - Useless?

Just a warning: UNSW Physics is very good in first year, but it is trash from 2nd year onwards (labs are hell as well). You will have to learn it yourself from websites like Mit opencourseware. UNSW completely ruined physics for me. So make sure you keep your comp sci degree as a back up...
17. ### 1967 HSC help

The left hand side is the average of (m+1) numbers {a^0,a^1,a^2,...,a^(m)} and the right hand side is the average of m numbers {a^0,...,a^(m-1)}. Since a^m is bigger than all the other numbers, having that present will increase the average. You can instead prove that adding a number greater...