Physics: Post your doubts here!

[Daniel Jeng]

I always use to do this shit at the end. xD I know it sucks when we stuck in the middle of the paper :/

I skipped the question immediately after getting stuck for one minute, finished the paper and agonized over that one question for 20 minutes XD turns out I had the right answer but I changed it at the very last second (although my reasoning wasn't correct anyways haha). Anyhow my physics teacher said if I had found it hard everyone would, so I guess I can live with it *shrugs*

 

[Thought blocker]

I skipped the question immediately after getting stuck for one minute, finished the paper and agonized over that one question for 20 minutes XD turns out I had the right answer but I changed it at the very last second (although my reasoning wasn't correct anyways haha). Anyhow my physics teacher said if I had found it hard everyone would, so I guess I can live with it *shrugs*

It isn't necessary that if u found it difficult everyone will face the same problem. Lol! Maybe others could do it very easily xD
Like if u didn't strike what u have to do maybe u are thinking very complex but answer is very simple xD IK this happens xD
Haha.. anyways god luck

 

[Daniel Jeng]

It isn't necessary that if u found it difficult everyone will face the same problem. Lol! Maybe others could do it very easily xD
Like if u didn't strike what u have to do maybe u are thinking very complex but answer is very simple xD IK this happens xD
Haha.. anyways god luck

That's true. The question had both capacitors and resistors in the circuit, which kind of threw me off. Even so with enough thinking I could've came up with the correct answer and correct thinking. Although it's not necessary that everyone will find it hard, I suspect the majority will as I had seen no question of that kind from seeing all papers 2011 onwards.

 

[Thought blocker]

That's true. The question had both capacitors and resistors in the circuit, which kind of threw me off. Even so with enough thinking I could've came up with the correct answer and correct thinking. Although it's not necessary that everyone will find it hard, I suspect the majority will as I had seen no question of that kind from seeing all papers 2011 onwards.

Can u share the question if u remember?.

 

[Astralgod]

If I remember correctly 4 is also somewhat of an awkward succession, so I would only go with 1,2,5 or 10 mostly.

Did my physics paper 4, screwed up a 4 mark question ._. the rest was alright, but that was kind of depressing getting stuck in the middle of the paper

So long as you get the coordinates on point it's fine. Scales which are definitely no-no is 3,6,9 or decimal,0.3 stuff like that.

 

[Astralgod]

Btw, can someone explain to do the graph question on paper 5 in general terms.

 

[Coolio_777]

W16 p11

correct answer is B but how?

 

[Daniel Jeng]

View attachment 62735

W16 p11

correct answer is B but how?

Firstly you would want to know what is the time taken for the cyclist to land at the bottom of the track.

You know that the acceleration is 9.81ms^-2 downwards, the initial vertical velocity, u, as 0, and the vertical displacement, s, as 2.0m. To find the time taken just use the equation s=ut+(1/2)at^2, and you can find time easily.

Now, as there is no acceleration in the horizontal direction, just use the formula v=s/t to find the horizontal velocity of the cyclist, and that will be the initial horizontal velocity as that velocity stays constant. The same time can be used because it takes the same time for the cyclist to fall down 2m as well as travel 6m across.

 

[Daniel Jeng]

Btw, can someone explain to do the graph question on paper 5 in general terms.

Hmmm, some of the tips might be as follows:

- Make sure, when plotting points, that the diameter of the crosses do not exceed one small square on the graph paper
- Both the line of best fit and worst fit needs to cover more than 50% of the graph both vertically and horizontally
- The worst fit line MUST cross every single error bar, therefore sometimes you cannot draw the worst fit graph in one particular way, but can in the other direction.
- Make sure you put the small "hats" on the error bars so the examiners can see clearly the boundaries of your error bars

That's the general things to keep an eye out for in the graphs. However for the tables and calculations:

- When you are writing the table, if there are no uncertainties associated with the value, express the values to 1 more significant figure
- All absolute uncertainties at 1 significant figure, and all values associated needs to be at the same place value
- Show one of your uncertainty calculations beneath the table, even if there's no space for it
- Log values do have units, for example if you log a length value, write the units in the table as e.g. log(d/m). Put the units within the log expression
- When asked for the uncertainty of the gradient, the absolute uncertainty will be the absolute difference between the gradient of the best fit and worst fit line
- When asked for the uncertainty of the y-intercept value, the absolute uncertainty will be the absolute difference between the y-intercept of the best fit and worst fit line

I think that's all I can remember. Are you sitting both AS and A2 level this year?

 

[Daniel Jeng]

Can u share the question if u remember?.

Here's a sloppy drawing I had drawn for the physics teacher while asking about it. The question asks for the change in the potential difference across AB and CD when the switch turns from X to Y.

 

[Astralgod]

Hmmm, some of the tips might be as follows:

- Make sure, when plotting points, that the diameter of the crosses do not exceed one small square on the graph paper
- Both the line of best fit and worst fit needs to cover more than 50% of the graph both vertically and horizontally
- The worst fit line MUST cross every single error bar, therefore sometimes you cannot draw the worst fit graph in one particular way, but can in the other direction.
- Make sure you put the small "hats" on the error bars so the examiners can see clearly the boundaries of your error bars

That's the general things to keep an eye out for in the graphs. However for the tables and calculations:

- When you are writing the table, if there are no uncertainties associated with the value, express the values to 1 more significant figure
- All absolute uncertainties at 1 significant figure, and all values associated needs to be at the same place value
- Show one of your uncertainty calculations beneath the table, even if there's no space for it
- Log values do have units, for example if you log a length value, write the units in the table as e.g. log(d/m). Put the units within the log expression
- When asked for the uncertainty of the gradient, the absolute uncertainty will be the absolute difference between the gradient of the best fit and worst fit line
- When asked for the uncertainty of the y-intercept value, the absolute uncertainty will be the absolute difference between the y-intercept of the best fit and worst fit line

I think that's all I can remember. Are you sitting both AS and A2 level this year?

Yep daniel. Also can you possibly run through how to drawn error bars and a worst acceptable line? Thanks in advance

 

[Daniel Jeng]

Yep daniel. Also can you possibly run through how to drawn error bars and a worst acceptable line? Thanks in advance

Error bars are just the absolute uncertainty of the values you have entered in the tables. e.g. if it's +/- 0.2 you would draw the error bar as having a length of 0.4, 0.2 above and below the plot point. However there are some cases where you draw horizontal error bars but that's determined by the table that you had been given and which variable's uncertainty you need to calculate.

For the worst acceptable line, draw from the bottom of the error bar of the first plot point to the top of the error bar of the last plot point. Conversely you can draw the line from the top of the first plot point error bar to the bottom of the last error bar. That'll give you the worst acceptable line. But like I said, make sure the worst acceptable line passes through every single error bar otherwise you will lose a mark. That's why you have two choices as to how to draw it.

 

[Astralgod]

Thank you man, much appreciated.

 

[Daniel Jeng]

Thank you man, much appreciated.

You're welcome currently not faring well with literature -.-

 

[Unknown202]

Water of depth 10m exerts a pressure equal to atmospheric pressure.
An air bubble rises to the surface of a lake which is 20m deep. When the bubble reaches the
surface, its volume is 6.0cm3
.

What is the volume of the air bubble at the bottom of the lake?
help plzzz

 

[Unknown202]

and
Microwaves are used to transmit television signals to and from a satellite.
Which statement about microwaves is correct?
A They have a longer wavelength than radio waves.
B They penetrate the atmosphere without significant loss of energy.
C They travel much faster than radio waves in a vacuum.
D They warm the satellite and stop it freezing.
why is it B

 

[A*****]

Water of depth 10m exerts a pressure equal to atmospheric pressure.
An air bubble rises to the surface of a lake which is 20m deep. When the bubble reaches the
surface, its volume is 6.0cm3
.

What is the volume of the air bubble at the bottom of the lake?
help plzzz

Use the equation P1V1=P2V2
At the surface, the pressure is 1 atm and the volume of bubble is 6cm3 and 20m below, the pressure is 2 atm.
So applying the equation, 1x6=2 x V2
V2= 1x6/2 =3 cm3

 

[A*****]

Btw if I'm not mistaken, this question is from O level Physics, right?

 

[Unknown202]

an

Use the equation P1V1=P2V2
At the surface, the pressure is 1 atm and the volume of bubble is 6cm3 and 20m below, the pressure is 2 atm.
So applying the equation, 1x6=2 x V2
V2= 1x6/2 =3 cm3

answer is 2???not 3

 

[A*****]

an

answer is 2???not 3

Ohh I'm sorry...pressure at the bottom will be 3 atm, not 2 bqz 2 is due to the water above and 1 of the atmosphere itself so yes it would be 1x6/3=2 cm3