HSC Tips - Mechanics (2 Viewers)

[Grizzly]

Jizz -

"- Know how to work out escape velocity using inverse square law for gravity"

Have i missed something ?? :O
Thats not in the Arnold book ?!

 

[McLake]

Originally posted by Grizzly
Jizz -

"- Know how to work out escape velocity using inverse square law for gravity"

Have i missed something ?? :O
Thats not in the Arnold book ?!

It's Physics, but you should probably know it for Maths

 

[freaking_out]

Originally posted by Newbie
ezzy here is also a good candidate for 100 in both maths

in fact, ezzy > affinity ! :evilwhip:

do they go to the same school?

 

[freaking_out]

Originally posted by OLDMAN
Use integral limits in solving mechanics rather than the more cumbersome 2-unit "integrate, add constant and check boundary conditions" way. See example in "trivial mechanics" thread.

adding onto this, i saw this other method where they incoporate the constant in the log....for example:

instead of v^2=ln(x^2+3)+C, where C is the intergration constant

they instead put:

v^2=ln(x^2+3)A, where A is a constant

c question 6 b (iii) of 2002 independent paper found on the other thread.

 

[heath]

"- Know how to work out escape velocity using inverse square law for gravity"


please explain. i always get escpae vel q's wrong, and coincidently i don't know the inverse square law u speak of

 

[McLake]

Originally posted by heath
"- Know how to work out escape velocity using inverse square law for gravity"


please explain. i always get escpae vel q's wrong, and coincidently i don't know the inverse square law u speak of

Inverse law says

g = k/r^2

so gravity is inversly proportional to radius squared.

 

[heath]

o is that all. most questions tell u that anyways.

i thought it was something to do with that physics equation; escape velocity= sqrt of 2GM/r

 

[ezzy85]

with these terminal velocty questions, is it enough to just say a = 0 and solve for v? or do you have to do all the integration with t and make t appraoch infinity?

 

[freaking_out]

Originally posted by ezzy85
with these terminal velocty questions, is it enough to just say a = 0 and solve for v? or do you have to do all the integration with t and make t appraoch infinity?

i think u make t go to infinity.

 

[heath]

nope our teacher alwasys lets a=o then solve for v.

cause when there is no acceleration it is at max velocity. u know that from 3 unit (SHM)

 

[freaking_out]

Originally posted by heath
nope our teacher alwasys lets a=o then solve for v.

cause when there is no acceleration it is at max velocity. u know that from 3 unit (SHM)

aren't we talking about resistive motion but?

 

[ND]

Originally posted by freaking_out
aren't we talking about resistive motion but?

Yes but when something reaches terminal velocity, its acceleration stops.

 

[vegeta_316]

Making t go to infinity and a=0 are both acceptable rules in determining terminal velocity. Just pick one determining on the question.

 

[deyveed]

With Resisted Motion, when they tell you that the resistance is proportional to v^2 for instance, do you assume in the eqn that the v^2 part is mkv^2 or just kv^2?

 

[Fosweb]

Depends on whether they mention if the object has a mass. If the object is massless (or of unit mass) then your equations are independant of mass (so F = ma becomes F = a)

 

[ezzy85]

you include the mass because it will be cancelled out eventually.

 

[deyveed]

Some questions in the textbook have mkv^2 and some just have kv^2.
Would the answer work out to be the same if you take either paths?

 

[McLake]

Originally posted by deyveed
Some questions in the textbook have mkv^2 and some just have kv^2.
Would the answer work out to be the same if you take either paths?

One is talking about a Force (with m), the other is talking about an acceleration (no m).

The m always ends up cancelled anyway (as easy85 said)

m should NOT appear in the final answer

 

[freaking_out]

i just had a look at the syllabus 2day, and i saw that they had some alright questions there....so its worth a look. also under harder 3u, the syllabus quotes some questions for circular geometry, which i saw was actually used in one of the trials.

 

[Hotdog1]

On the mkv/kv thing, it depends on what the question describes the term to represent. I've seen questions when they said the resistive FORCE is kv^2, therefor the mass m is incorperated in kv^2.