Will the real TeeEm please stand up!

Original post by TeeEm

it happens ...
well you learned a bit and I have another nice question to add to my books
:smile:

Thank you. :smile:

Reply 1781

OP

Original post by edothero

is

|SP| + |TP| = 2a

a loci property of an ellipse?

Was never taught that :colonhash:

not only you ought to know it but it is examinable !!!

Reply 1782

Original post by edothero

is

|SP| + |TP| = 2a

a loci property of an ellipse?

Was never taught that :colonhash:

Though to be fair it is quite obvious..

Yep, it's in the FP3 textbook, went over it a few days ago.

Reply 1783

edothero

15

Original post by TeeEm

not only you ought to know it but it is examinable !!!

Thank you anyway.

Reply 1784

OP

well pleasing ... thanks to the people which nominated me and also voted for me
http://www.thestudentroom.co.uk/showthread.php?t=3889039

6 nominations ... two firsts, two seconds and two thirds ....

Thank you again

Reply 1785

GeologyMaths

2

Original post by TeeEm

well pleasing ... thanks to the people which nominated me and also voted for me
http://www.thestudentroom.co.uk/showthread.php?t=3889039

6 nominations ... two firsts, two seconds and two thirds ....

Thank you again

Calm tf down, its only a forum site

Reply 1786

OP

Original post by GeologyMaths

Calm tf down, its only a forum site

you are clearly very jealous ...

Reply 1787

Someone help? Found this question on Variable Acceleration in 2 dimensions and don't understand how they get values of maximum and minimum acceleration for part b. I managed to get a=12 using the given rearrangement, but don't know how to get the maximum!

Posted from TSR Mobile

1455318828729.jpg16.2KB

Reply 1788

OP

Original post by Hassan55

Someone help? Found this question on Variable Acceleration in 2 dimensions and don't understand how they get values of maximum and minimum acceleration for part b. I managed to get a=12 using the given rearrangement, but don't know how to get the maximum!

Posted from TSR Mobile

@Zacken @SeanFM @16Characters....

do you mind please

(edited 8 years ago)

Reply 1789

Original post by Hassan55

Someone help? Found this question on Variable Acceleration in 2 dimensions and don't understand how they get values of maximum and minimum acceleration for part b. I managed to get a=12 using the given rearrangement, but don't know how to get the maximum!

Posted from TSR Mobile

Let the acceleration be $a$ , then acceleration will achieve minimum and maximum values when $\frac{da}{dt} = v = 0$ , so find the values of $t$ for which this is so, investigate whether they are minimum or maximum values by considering the second derivative and then plug it back into the equation to find the min/max acceleration.

Edit: ignore this, as per SeanFM, recall that

\cos^2 x

varies between

0

and

1

...

(edited 8 years ago)

Reply 1790

Original post by TeeEm

Aye

OP

Original post by Zacken

Aye

thank you

Reply 1792

Kevin De Bruyne

21

Original post by Hassan55

Someone help? Found this question on Variable Acceleration in 2 dimensions and don't understand how they get values of maximum and minimum acceleration for part b. I managed to get a=12 using the given rearrangement, but don't know how to get the maximum!

Posted from TSR Mobile

Look at the expression and think the smallest and largest value that it can take.

Reply 1793

Original post by Zacken

Let the acceleration be $a$ , then acceleration will achieve minimum and maximum values when $\frac{da}{dt} = v = 0$ , so find the values of $t$ for which this is so, investigate whether they are minimum or maximum values by considering the second derivative and then plug it back into the equation to find the min/max acceleration.

Edit: ignore this, as per SeanFM, recall that

\cos^2 x

varies between

0

and

1

...

Why do you put v=0,can't you put a=0 and instead of using the suggested expression, can't you use dv/da=a=0 and solve for t in both i and j. Is there any other approach,ie with the expression they give, to solve this?

Reply 1794

Original post by Hassan55

Why do you put v=0,can't you put a=0 and instead of using the suggested expression, can't you use dv/da=a=0 and solve for t in both i and j. Is there any other approach,ie with the expression they give, to solve this?

I don't know what I was thinking, but da/dt is not v... , themethod you propose would find the maximum/minimum velocity, not acceleration. You could differentitate the position vector they've given you *four* times and set thag equal to 0, but it's a lot of work when you can just look at how cos x varies from the dervived expression!

Reply 1795

My proposed method seemed to have worked surprisingly, where I set the i and j components of a to 0 and worked out values for t to get 12 and 14. I used the method similar to this mark scheme.. you're right saying a=0 will give max/min velocity, but how come they do this?

Posted from TSR Mobile

1455325304130.jpg46.7KB

Reply 1796

Also I differentiate 4 times (only had to do it twice more because of part a) and got tan(2t)=-4/3... And by getting t I didn't get 12 or 14 :/

Posted from TSR Mobile

Reply 1797

Original post by Hassan55

Also I differentiate 4 times (only had to do it twice more because of part a) and got tan(2t)=-4/3... And by getting t I didn't get 12 or 14 :/

Posted from TSR Mobile

Oops, did I say 4 times? My mistake, it was really late at night and I was in bed. Differentitate once to get velocity, second time to get acceleration, third time to get jerk and then that =0. So differentiate thrice, not four times.

Reply 1798

Do you differentiate a naturally as you keep differentiating from r or do you differentiate the expression the give you?

Posted from TSR Mobile

Reply 1799