mechanics 18th/oct 2010 discussion

[Zazzyo]

I got T1=10 and T2=30 .. and was getting speed 100 sumthing.. quite unbelievable.. but i double checked many times..... And for Q5 i somehow got the answers 112 m/s and 113 m/s for mand q resp... which is wrong i am sure.. And what was the magnitude of F in the forces question where alpha was 84 sumthing....

And the graph for Q7 had two stationary points.. it had a curvy N shape.. and v=5 m/s at t=o

 

[cyberoxis]

Q5)b)
s=ut + 1/2 at^2 write the equations of ""s"" for both particles and equal them

but the tricky part was tht q had started 0.4s later than p

so i managed to find the distance travelled by p for the 0.4s
it was 7.2m .. then altered the equations

solved the equations and got t=1.44s where t is the time where both particles are at same height
using formula v=u+at
i got velocity of p = 5.6 m/s
q = 10.6 m/s

is it correct?

haha wrong like everone did.... the value of u for the particle when it is at t=0.4 is not 20 but 18.... so it 18t - 5t^2 + 7.2....

 

[zeny]

hey guys i'm from brunei and i do paper 43? any idea about it??

 

[adzino]

Ok i dont remember much but i am trying my best to recall..
Question 1
force around 2000N acting 15 to the vertical upwards.
object of mass 400kg.
the object is in limiting equilibrium
find the coffecient of friction

question 2
something about work power energy i dont remember

question 3(was tricky for me)
i guess the angle was 83-84 degree...force i dont remeber

question 4
this also i dont remember much probably work power energy

question 5
particle P and Q question. part ii was a bit confusing i missed 5 marks over here cuz i didnt get the time to solve

question 6

graph question
velocity i guess V=6
t=8.5s
others i dont remeber

question 7.

t1=10, t2=30
distance is 285 m (i dont remebr exectly)

and what else...i can remember upto this much

ans 1 was 0.25...ans 3 F=5.52.....hey...can you remind me how the figure of question 6 actually was..

um a triangle below the x axis and a trapezium above i guess..

 

[MasterOfPuppets]

Q5)b)
s=ut + 1/2 at^2 write the equations of ""s"" for both particles and equal them

but the tricky part was tht q had started 0.4s later than p

so i managed to find the distance travelled by p for the 0.4s
it was 7.2m .. then altered the equations

solved the equations and got t=1.44s where t is the time where both particles are at same height
using formula v=u+at
i got velocity of p = 5.6 m/s
q = 10.6 m/s

is it correct?

haha wrong like everone did.... the value of u for the particle when it is at t=0.4 is not 20 but 18.... so it 18t - 5t^2 + 7.2....

I assume he's correct, I recall 5.6 and 10.6 or something similar. However, you misunderstood as basic concept. "u" means the initial speed. T is the time. If you calculate time to be 0.4, you HAVE to place the initial speed as 20, because that is the initial speed of the entire journey relevant to the starting point, 0.4 seconds after the initiation. If you wanted to use it as 18, you have to put the t as 0 and consider that particular point where the speed is 18 m/s the starting point of the journey you are studying.

 

[Afghan]

Question 3
I think i got the angle as 81 by resolving vertical and horizontal forces. The last thing was Tanֿ1 of something.
Question 5
Missed the whole thing! :evil:
Question 6
I got v=6 and t=8.5 like 'Adzino' said.
Question 7
T1=10, T2=30 and S=105 metres. It was a whole lot of differentiation and integration in this one.
Graph part, not sure about it, but did make a bunch of lines in it.

Overall I beleive I might lose around 10 marks, but still it was a bit tough so hopefully the GT would be low this time, like around 36, hard chances though. :roll:

 

[ubhek]

question 6...can any one remind me the triangle...0-2 or 0-2.5....and the time of rest....and the last point on the x axis...was it 12.5 or 14.5....on t.

 

[nirajgrg]

Question 3
I think i got the angle as 81 by resolving vertical and horizontal forces. The last thing was Tanֿ1 of something.
Question 5
Missed the whole thing! :evil:
Question 6
I got v=6 and t=8.5 like 'Adzino' said.
Question 7
T1=10, T2=30 and S=105 metres. It was a whole lot of differentiation and integration in this one.
Graph part, not sure about it, but did make a bunch of lines in it.

Overall I beleive I might lose around 10 marks, but still it was a bit tough so hopefully the GT would be low this time, like around 36, hard chances though. :roll:

i got s=285 for question no. 7

 

[nirajgrg]

Q5)b)
s=ut + 1/2 at^2 write the equations of ""s"" for both particles and equal them

but the tricky part was tht q had started 0.4s later than p

so i managed to find the distance travelled by p for the 0.4s
it was 7.2m .. then altered the equations

solved the equations and got t=1.44s where t is the time where both particles are at same height
using formula v=u+at
i got velocity of p = 5.6 m/s
q = 10.6 m/s

is it correct?

i got this one wrong too, but i guess the correct answers are velocity of p=8 and q=17 as my friend mentioned

 

[usamazee]

question 5b) i got t=1s and p=10 and q=11

 

[Frooty]

hey cyberoxis ... !!!
just think for urself , get a general approximation. speeds of p and q were 20 and 25 m/s respectively
they undergo retardation of 10 m/s^2
so in 1.44 sec their velocities would b ranging 5-11 respective
so i guess i stand a lil chance here. i got for p= 5.6 m/s
for q= 10.6 m/s


please reply ur views if u think last question was hell tricky and percentile would get really low
tanx

 

[cyberoxis]

every thing was easy.... in fact in question five one can avoid all the confusion if one translates the displacement function by 0.4.... was doing in this manner but a stupid calculation in the end turned it's head against it.... and i can't for the life think how could i doubt the credibility of this method.... another way tried was just as yours but the lack of time precluded the chance to change the speeds since now the initial motion starts at t = 0.4 .... well the last one was an extremely easy but messy example of what can come in paper.... 0.002t^3 - 0.12t^2 +1.8t + 5 differentiate and t = 10 and t =30 and integrate to get OP = 285 and the graph is smooth cubic curve with all that crap of derivatives and no mechanics.... guess that examiners are loosing what mechanics and truly Newtonian Mechanics dealt with and what Einstein's Quantum mechanics was looking for....

 

[MasterOfPuppets]

every thing was easy.... in fact in question five one can avoid all the confusion if one translates the displacement function by 0.4.... was doing in this manner but a stupid calculation in the end turned it's head against it.... and i can't for the life think how could i doubt the credibility of this method.... another way tried was just as yours but the lack of time precluded the chance to change the speeds since now the initial motion starts at t = 0.4 .... well the last one was an extremely easy but messy example of what can come in paper.... 0.002t^3 - 0.12t^2 +1.8t + 5 differentiate and t = 10 and t =30 and integrate to get OP = 285 and the graph is smooth cubic curve with all that crap of derivatives and no mechanics.... guess that examiners are loosing what mechanics and truly Newtonian Mechanics dealt with and what Einstein's Quantum mechanics was looking for....

Mind you, mechanics is based on pure math. And that question was a fine example of how well they can intertwine. The question was as much mechanics as it should be. It just requires some proficiency is pure topics. I don't see how they're losing what mechanics dealt with.

 

[cyberoxis]

Dear friend or Master of puppets,
Let me tell you something of grave concern. Lagrange wrote his Mechanique Analitique in a painful period of 25 years and could in the end boast it to be a part of pure mathematics and magnum opus of rigor that not even a single diagram appeared on it's paper. When a mathematical discipline is designed, it does not require any diagrams or visuals to state what is intended. Only axioms should suffice. The CIE is maneuvering to make papers appear "hard" and as you say " fine " while in fact the true name is " messy". Dealing with long pure algebra and messy polynomials which even the greatest and most proficient of mathematicians will not heed to is called computation. Mathematics is far way off from the intimate airways of your baffling mind. There are thousands of problems not exercises which you dwell to do and you always remain in that dwelling. And if you think you have not thrown the gauntlet yet, join the community of mathlinks.ro and many would be pleased to shake your notions without repeating anything ad nauseum.

 

[grimreaper_123]

wow cyberoxis...u in luv wid maths or sumfin?