Forumers, ask your Physics questions here ! (compilation)

Flying grenade SG

Please feel free to post your Physics questions here ! Let us all ask, discuss, and contribute in this Homework Forum @ SGForums ! :D

Flying grenade SG

[For H2 Physics(and H2 math)]

MightyBiscuits asked : Why is it that for a small θ , sinθ = tanθ = θ?

read and study this : https://en.m.wikipedia.org/wiki/Small-angle_approximation

Flying grenade SG

[For H2 Physics]

MightyBiscuits posted regarding Work,Energy,Power & Forces qn,

addressed by eagle and Flying grenade, with extension questions by eagle

MightyBiscuits SG

Thank you very much. May I also enquire if this also applies in a small change in mass?

eagle SG

Small angles approximations will be taught in your J1 Maths.

You have to go through Differentiation, Applications of differentiation, Maclaurin's Series first before learning small angles approximations. Most schools shouldn't have reached yet.

Small angle approximations in Physics are generally not tested at H2 Physics level anymore. If they do test, they should provide you with the approximation. The question you have shared is a very very old question, probably outdated.

Flying grenade SG

[For H2 Physics]

MightyBiscuits asked :

https://www.instagram.com/p/BHcq0BRhvew/?taken-by=lolwerwdr

For CS Toh physics practice Qns 4(ii) (Oscillations)

Flying grenade's suggested solution

Qn already given you the equation for the Period of oscillation of a spring-mass balance.

T=2π(m/k)^0.5

Qn already given u the values required, both m and k.

find period of oscillation before and after the astronaut gains 0.5kg by simple substitution and calculation.

for % change in period of oscillation, take (finalT - initialT)/initialT x 100%.

from wiki : " The small-angle approximation is a useful simplification of the basic trigonometric functions which is approximately true in thelimit where the angle approaches zero."

for this question scenario, whereby we attempt to calculate mass by method of oscillations, small angle approximations is inapplicable and irrelevant.

Flying grenade SG

Thank you very much. May I also enquire if this also applies in a small change in mass?

BTW MightyBiscuits, does Cstoh's physics practice qns book come with worked solutions either at the back of the book, after the chapter, or anywhere in the book ?

Flying grenade SG

For H2 Physics, and actually all subjects examined by SEAB&Singapore-Cambridge examinations,

the Syllabus(which can be found at SEAB's website) , is highly useful.

peruse and digest the great content outline and assessment objectives, which is truely a great summary,overview,and synopsis, and also Examples of the application of concepts and information in real life, making the Syllabus a very interesting, useful, and valuable read.

eagle SG

Hi,

the syllabus, while great, isn't an accurate representation of the question patterns that might be tested. Relying on it solely is pretty dangerous. It's a good guideline, not a summary.

Thanks :)

Flying grenade SG

Thanks eagle !!!

yes i agree for physics, chemistry ,biology and maths,

exposing to and doing many questions is very important.

exposing to new, different, atypical and unusual questions are fun and satisfying and ultimately helps very much in the preparation towards the national examinations.

iSean SG

Thermal Physics - Continuous Flow

Just wondering how do they make the temperature change constant though? Despite adjusting to increase the flow rate of water and voltage of heating coil for 300 seconds? New input of water is always replaces the heat away from the water.

The temperature change shouldn't be constant though?

Or is they just want to collect the constant the change of temperature by adjusting it only? Like Set 1 : Ti 25'C, Tf 35'C and Set 2 is adjusted to Ti 30'C and Tf 45'C

Also is it even possible to increase flow rate? As I thought mass flow in a tube is always constant in Fluid Dynamics?

eagle SG

I don't understand the first part of your question. The temperature change refers to the difference in temperature between the input and output of the tube.

It is possible to increase flow rate. Imagine this: you turn on your tap a little, vs turn on a lot. There is no such rule that mass flow is always constant in Fluid Dynamics. The closest you have, for water which is incompressible, is the continuity principle, where the volume in equals the volume out per unit time.

More volume in per unit time means more mass flows through in per unit time. Consequently, the thermal energy required per unit time (and hence power) needed to raise the temperature between the input and output will be higher, because heat capacity is proportional to mass.

iSean SG

Actually I'm quite uncertain regarding the steps of doing this experiment to determine specific heat capacity.

From what I can see here is my time is fixed, and my temperature change is fixed.
What are changed are my flow rate and power output.

Procedures:
1. Set up the apparatus as shown.

Collection of Set I
2. Run water at a constant flow rate until the two thermometers at water input and output zone reach a constant value, And this will be me "temperature change"?
3. Then I start timing for 300s?
4. Also collect Mass of Liquid collected, M1, Voltage, V1 and Current, I1 at this moment for 300s?

Collection of Set II
5. Run water at a higher flow rate, and adjust power by rheostat, until the two themometers reaches the same temperature change as Set I, then I collect the data again?

The book didn't really explain how they do the procedure tho.

Flying grenade SG

Hi iSean, may i ask u from which book/source are the questions in the 2 pictures u posted above from?

domefossil SG

Basic sf question (H2):

Flying grenade SG

in response to domefossil's question

for this qn, the value of the quantity should be rounded off to no decimal places , i.e. 231mm(0 dp) . This is because, the uncertainty of this quantity have no decimal places.

if for example, x is given to be x=18.0 , and y=12.5, then your final value of r must be rounded off according to the no. of decimal places of the uncertainty.

i didn't calculate your numerical working, assuming your numerical working is correct, the value of Δr you have calculated should be correct, i.e. 20mm(1sf round up)

Δr/r =Δx/x + Δy/y is the right formula to use.

you cannot calculate Δx/x and Δy/y and round up to 1sf first then add (even if u did, which is the wrong way, you'll still get 20mm(1sf) coincidentally) ,

only round up 1sf after u get Δr .

Flying grenade SG

Cambridge will unlikely ask you for the calculated value of fractional uncertainty.

They will most probably ask you to calculate the value of actual uncertainty.

If they did ask , the value of fractional uncertainty should be given as 0.067(2sf round up)

Flying grenade SG

percentage uncertainty must be rounded up to 2sf.

domefossil SG

percentage uncertainty must be rounded up to 1sf.

For this question only or as a rule of thumb?

Not necessarily specific to this question, is there a rule on how many sig figs to use for raw quantities? Is it ok to present a half answer like Δr/r as 0.5/18.5 + 0.5/12.5 = 0.067027027, if it's not the final answer to the question? Thanks bro.

Flying grenade SG

percentage uncertainty must always be rounded up to 2sf.

if it's not the final answer to the question, you can give that long string of values. or u can give all intermediate workings to be 5sf.

My Apologies, if Cambridge do ask you for fractional uncertainty, give it to 2sf(round up)

intermediate workings for fractional uncertainties should be given as 5sf or more sf,

cannot round up to 1sf for intermediate workings , lest your final calculated value will be inaccurate and thus incorrect.