A Physics thread of the QCE students, feel free to ask any questions!

Anyone is welcome to answer ๐Ÿ™‚

15 days later
a month later

Hehe, first question, here we come!

What is the difference between these two formulas?:

v_y = gt + u_y

v_y^2 = 2gs_y + u_y^2

Thanks,
-jinx_58

    jinx_58 I'm assuming these are the SUVAT formulas v = at + u and v2 = u2 +2as. You use each to solve for different variables depending on what info the question gives you. The 1st one isn't very useful for solving for s and similarly the 2nd one isn't very useful for solving for t since they don't contain the variable in them

        Thanks Billzene

        I'm having trouble with this projectile motion question from my textbook.
        I got the answer wrong and I don't know how

        Question: A marble travelling at 2.0m/s rolls of a jump, angled at 30 degrees above horizontal, and takes 0.75s to reach the floor.
        a) Calculate how far the marble travels horizontally before landing -> got this one correct
        b) Calculate the vertical component of the speed of the marble as it lands
        I got -6.35m/s for this one, but the textbook stated -2m/s
        Consequently, the answer to b affects c
        c) Calculate speed of marble as it lands
        I got 6.58m/s, but the textbook said 2.23m/s

        -jinx_58

          Just had a crack at this question, I've got what you've got too. Their suggested solution for part c makes no sense, since the horizontal component remains 2 x cos(30ยฐ) = root(3) m/s the entire time and they're saying the vertical component when it's landing is -2 m/s, then by pythag you'd expect v = root(((2)2 + (root(3))2)) = 2.65 m/s (also they asked for a speed which is a scalar quantity but they wrote it as a velocity/vector with the sign convention, dunno why they did that)

          The textbook is a little dodgy, thanks Billzene

          -jinx_58

          I actually also remember seeing this question in my textbook yesterday and got the exact same answers as you, jinx. I think it's pretty safe to say at this point that the textbook has stuffed up lol

          Question: What is the importance of symmetry in the standard model? If we haven't covered it in class, what are the basics that I would need to know for the exam?

            poppy
            I had the exact same question. From the study guides I've read, there's basically 3 types and they're quite easy to understand. But only revise if you have time to. I did the ATARnotes topic test for Standard Model, and one of the questions were, "Describe the significance of symmetry in particle interactions" (3 marks)

            This is what the marking scheme stated:
            "Symmetry operations are important as they reveal more about the universe, and provide a foundation for many fundamental laws of nature. They allow physicists to determine a specific interaction will take place, and always conserve both energy and momentum. Whilst violations of symmetry do occur, that cannot be considered laws of nature, these violations only provide further insight into particle interactions. Examples include charge/time reversal and crossing symmetry," - Charlotte Elgey and Tequile Ryan 2021

            Honestly, that dot-point is just so vague (typical QCAA). The key is just to provide as much info as you can to maximise the amount of marks in the exam. Having somewhat of an idea of the types of symmetry gives you an edge, as it helps to understand what's going on. However, this will not be directly assessed.

            Hope this helped,
            -jinx_58

              10 days later

              I did this magnetic field question...except I got the wrong answer and I don't know how.

              Calculate the magnitude of the magnetic field strength at point C, given that C and D are 3cm apart and make a 45ยฐ angle with the wire. The wire is carrying a current of 2.0A.

              I am unsure whether I should break it down into vectors, but if so I don't know how.

              I got 1.33 x 10^{-5} Teslas.

              Could someone please help out?

              Thanks,
              -jinx_58

              • God replied to this.

                jinx_58

                Is there an image by any chance?

                That usually makes these questions easierโ€ฆ

                    God
                    I really wish I could but for some reason I just can't chuck it up here.

                    Its like two lines intersecting and making a 45 angle and current flows this way <--

                    Idk if that makes sense

                    -jinx_58

                        jinx_58
                        Hey jinx_58,

                        I agree with @God here. It is a bit hard without the image. Is it possible you could upload it somewhere and then send a link of the image? Let me know if that's an issue.

                        • PP

                          Awesome, it works - thanks for the image. I just did the question and I got 1.89x10-5 T. If that's right, let me know so I can write out my working out but if its wrong, then I won't waste anyone's time ๐Ÿ˜…. I used B=ฮผI/2ฯ€r.

                          Hope that helps.

                          • PP

                            I need help with magnetic fields.
                            I think I mostly understand the theory. The problem is...well the problems. ๐Ÿ˜…

                            There are these questions which want you to find the force acting on one wire, when there are two other wires. Three wires in total, represented by dots or crosses, depending on direction of magnetic field. I understand how to find the magnitude through vector addition. But for the direction, the worked solutions generate a whole damn new triangle and I'm really heckin confused as to where they got it from. Like, how'd you get that angle? How'd you figure out that direction arrow? Why is the direction from the horizontal...and given in an angle????? What happened to up the page, down the page, into the page and out of the page???

                            Sorry for the rant, but my mind is teeming with questions.
                            Here's an example question:
                            https://imgur.com/a/Tl0aqWl

                            If someone could explain it in depth and address my questions above it will be very greatly appreciated, as I am really struggling to wrap my head around this concept. And my exam is in 27 days, and I'm behind on my Physics timetable. ๐Ÿ˜

                            Thank you so much in advance,
                            -jinx_58