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Mathematics: Post your doubts here!

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I need some serious help in mechanics. In a question regarding the work done = change in total energy, I don't understand how to decide which one from K.E and P.E has a greater value so that I can subtract well. Please pleaseee help me understand the concept.
Here is an example:
http://papers.xtremepapers.com/CIE/...S Level/Mathematics (9709)/9709_s10_qp_41.pdf
qn no. 5(ii).. how do you decide which one (K.E/P.E) has a greater value?

I'll really reallyyy appreciate any help provided.

Thanks a lot
 
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I need some serious help in mechanics. In a question regarding the work done = change in total energy, I don't understand how to decide which one from K.E and P.E has a greater value so that I can subtract well. Please pleaseee help me understand the concept.
Here is an example:
http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Mathematics (9709)/9709_s10_qp_41.pdf
qn no. 5(ii).. how do you decide which one (K.E/P.E) has a greater value?

I'll really reallyyy appreciate any help provided.

Thanks a lot
I will explain you th whole concept and try to understand ...
First thing you need to consider , is to know if surface is smooth/ rough ( has friction )by reading question.
then follow the formula wd (workdone ) by driving force = wd by resistive force ( resisting motion ) +- K.E gained/lost +- P.E gained/lost.
if it increses in speed KE is gained ( Add in eqn ) if decreased in speed its decresed KE is lost ( subtract from eqn )..
If it increses in Height ( moves up ) PE is gained ADD in eqn ... and if comes down PE is lost and subtract in eqn
so when something is gained ADD and when lost MINUS as you see i wrote +- in eqn depending whether its lost or gained .
we know wd formula is = F * d

In this question ,,, here its same speed .. mean no gain/loss in KE .. so its not included in equation and there is no Wd by driving force so both are ZERO in eqn
So our eqn is wd (workdone ) by driving force = wd by resistive force ( resisting motion ) + K.E + P.E gained
0 = 0.39 + 0 + mgh
 
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I will explain you th whole concept and try to understand ...
First thing you need to consider , is to know if surface is smooth/ rough ( has friction )by reading question.
then follow the formula wd (workdone ) by driving force = wd by resistive force ( resisting motion ) +- K.E gained/lost +- P.E gained/lost.
if it increses in speed KE is gained ( Add in eqn ) if decreased in speed its decresed KE is lost ( subtract from eqn )..
If it increses in Height ( moves up ) PE is gained ADD in eqn ... and if comes down PE is lost and subtract in eqn
so when something is gained ADD and when lost MINUS as you see i wrote +- in eqn depending whether its lost or gained .
we know wd formula is = F * d

In this question ,,, here its same speed .. mean no gain/loss in KE .. so its not included in equation and there is no Wd by driving force so both are ZERO in eqn
So our eqn is wd (workdone ) by driving force = wd by resistive force ( resisting motion ) + K.E + P.E gained
0 = 0.39 + 0 + mgh
Thanks a lot for the explanation, I really appreciate it.
I understood what you said about adding/subtracting the P.E/K.E values but I still don't get when you have to do (K.E - P.E) or (P.E - K.E).. how do you know which one is greater than the other?
Regarding the question paper that I had linked, the marking scheme actually calculates the K.E lost which opposes your previous statement. If you have any other explanation about why they used W.D = P.E gained - K.E lost + w.d against friction, please help me out.

Thanks :)
 
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Does anyone know some website from where I can get A-levels revision notes? I'v lost mine and the xtreme papers revision notes are not available:(
 
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A stone is projected vertically upward with a speed of 21 m/ s .find the distance travelled by the stone in the first 3 seconds of its motion . Plzzz anyone help me out
 
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