Physics formulas and common exam tricks (1 Viewer)

[banipal753]

Well, often in exams, we are given certain questions that require you to either adapt the provided information (convert cm^2 to m^2....mV to V) or use a certain formula (sometimes not provided on the formula sheet)

What are some common exam formula's/info adapting in the exams?

 

[untouchablecuz]

when doing mathematical questions relating to special relativity use your common sense

e.g. we know that as v->c, the mass of an object will increase

so if we're doing a Q, and it asks for the relativistic mass - if the value we get is smaller, then obviously we have mis-assigned m and m₀

same applies for time dilation and length contraction

 

[banipal753]

i consider the subscript O in m to be observer and we need to find the relativistic mass. That helps me remember. Thanks for that mate

 

[untouchablecuz]

also, know how to derive some formulae; such as orbital velocity and keplers 3rd law

 

[banipal753]

derive? how are they derived?

 

[banipal753]

Untouchablecuz is that Lamassu the Assyrian wingedbull in ur avatar i see

 

[untouchablecuz]

for orbital velocity, equate centripital force and gravitational force

F_c=F_g
mv²/r=GM_planetm/r²
v_orbital=√(GM_planet/r)

for keplers third law, let, in the above equation, v_orbital=2πr/T

 

[untouchablecuz]

Untouchablecuz is that Lamassu the Assyrian wingedbull in ur avatar i see

noo

your mistaken

;]

 

[banipal753]

lol oh my apologies

 

[untouchablecuz]

only joking

 

[banipal753]

Thanks for the help bro

 

[annabackwards]

for orbital velocity, equate centripital force and gravitational force

F_c=F_g
mv²/r=GM_planetm/r²
v_orbital=√(GM_planet/r)

for keplers third law, let, in the above equation, v=2πr/T

Reminds me of mxt2 aha, but yeah you need to know it.

General exam tips:

• Check that everything is in SI units before calculating equations!
• Include and equation if possible
• Learn a concise definition for your laws because they usually ask for them - ie Lenz's, Faraday's and laws of conservation of mass/momentum
• Maths students, make sure your calculators are set to degrees and not radians XD
• Read graphs carefully, taking note of the units on each axis
• For quanta, make sure LHS = RHS for bottom and top numbers for nuclear reactions and be especially careful with beta decay!

 

[untouchablecuz]

also, understand the meaning of the term proportional and how you can use equations to answer questions

e.g. why does the value for gravity decrease as one moves farther away from the centre of the earth?

g=GM/r²

from here, we can see that g is inversely proportional r²

.'. if r decreases, then g will increase and vice versa

in this case, increasing the distance away from the centre of the earth will result in the value for r increasing, and thus the value for g decreasing