# Physics: Post your doubts here!

#### PlanetMaster

Sorry to disturb you again and again but can you pls tell that how the graphs are intersecting at 0.5 and 0.8
No worries pal. For both waves, we can take the points they intersect 0 displacement in the same direction.

Like this:

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• Screenshot 2023-03-21 132418.png
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#### Lemniscates

PlanetMaster can u pls explain this uestion? thankyou!
Hey redox233, I am not sure if you still need help on this, but let me explain this to you:-

[imath]\rightarrow[/imath] This is a classic problem of standing waves.
[imath]\rightarrow[/imath] Given that the lowest sound produced is [imath]92[/imath] Hz, such as a node at the mouthpiece and an antinode at the other open end.

Hence, this is what we have,

We know that distance between a node and an antinode is [imath]\lambda/4[/imath].

[imath]\therefore \lambda/4[/imath] corresponds to [imath]92 \space \mathrm{Hz}[/imath].

The next arrangement of the standing wave to produce another frequency is as follows,

Here, we have [imath]\lambda/2 + \lambda/4 = 3\lambda/4[/imath]

[imath]\therefore 3\lambda/4[/imath] corresponds to [imath]3 \times \lambda/4 = 3 \times 92 =[/imath] [imath]276 \space \mathrm{Hz}[/imath]

Here is the next arrangement and you can follow this idea to get the overall correct answer to this question,

Here, we have [imath]\lambda + \lambda/4 = 5\lambda/4[/imath]

[imath]\therefore 5\lambda/4[/imath] corresponds to [imath]5 \times \lambda/4 = 5 \times 92 =[/imath] [imath]460 \space \mathrm{Hz}[/imath]

[imath]\rarr[/imath] If you simply look at all the options now in the question, we can clearly see that C seems to be the correct option.
[imath]\rarr[/imath] However, feel free to visualize the next arrangement and its corresponding frequency and match it with option C.

I hope this helps.
Good luck!

#### Lemniscates

No worries pal. For both waves, we can take the points they intersect 0 displacement in the same direction.

Like this:View attachment 70545

Hey PlanetMaster,

What software do you use to create such graphs that go with the background of the XPC theme? 🤔
Also, it would be great if you could provide a Math editor in the options so that we don't have to externally use LaTeX to write Mathematical equations here.

Thank you! ^_^

#### unknownerror21

a child of mass 35 kg movies down a sloping path on a skate board. the sloping path makes an angle 45 degree with the horizontal. the constant speed of the child along the path is 6.5 m/s. Calculate:
a) vertical dist through which child moves in 1.0s (done)
b) the rate at which potential energy is being lost (g=9.81 m/s^2) (confusion)

How is the answer to b) 80 J/s??

All I did was P = (35x9.81x0.51)/1 which gives answer 175 J/s (or 175 W)

a child of mass 35 kg movies down a sloping path on a skate board. the sloping path makes an angle 45 degree with the horizontal. the constant speed of the child along the path is 6.5 m/s. Calculate:
a) vertical dist through which child moves in 1.0s (done)
b) the rate at which potential energy is being lost (g=9.81 m/s^2) (confusion)

How is the answer to b) 80 J/s??

All I did was P = (35x9.81x0.51)/1 which gives answer 175 J/s (or 175 W)
A)
vertical distance moved: sin(45)=6.5/dist
dist = 0.7071*6.5
dist = 4.596

B)
rate at which potential energy is lost is just the energy change in one sec (i.e. vertical dist change in part A)
p.e = mgh = 35*9.81*4.596
p.e. = 1578 J/s

#### Hannah Moore

Hey everyone, if a person gets a wrong trend in the values in P3 physics Q.1. What is the procedure of marking for them.

#### Lenny Lino

Can I still fail if I pass? I must know, very important, what if I fail after I pass?? But I passed when I failed??!!? Tell me NOOOOOW, I am passing with fail on my exam tomorrow?