Is this the method that anyone else used for Q8? Not sure where I went wrong.

No KEs to consider first of all. Now by conservation of energy,

GPE+EPE before = GPE+EPE+Work after

Taking x to be the distance from A when next at rest, height for GPE is x/2. (xsin30.)
This is taking the 0 GPE level to be at the point when next at rest.

EPE is for one string, since extension 0 for one string, extension 5 for the other so EPE from that string.

Because of our choice of GPE level, GPE=0 after.

EPE after is total of the two EPEs for both strings, so with extension of x in one of them and extension of x-6 in another.

Work found by x multiplied by coefficient of friction multiplied by reaction force which is mgcos30.

Then I got two answers, chose the larger one, added 4 (got 7.05m).

I did the same as you, but chose the smaller value of x, so got 5.20 m instead of 7.05m.

Reply 246

ThusSpakeAlex

How many UMS would 68/69 marks be?

Reply 247

Hjyu1

Original post by ThusSpakeAlex

How many UMS would 68/69 marks be?

I'm thinking similar to 2014 so like that

Reply 248

jjsnyder

Original post by rainbowtwist

Did anyone else at all get (1 - mu)/4mu

Got that first time. Then corrected myself and got the right answer.

Posted from TSR Mobile

Reply 249

maisym00

Original post by jjsnyder

Got that first time. Then corrected myself and got the right answer.i

Posted from TSR Mobile

What is the correct answer

Reply 250

ThusSpakeAlex

Original post by Hjyu1

I'm thinking similar to 2014 so like that

Seemed harder than 2014 imo.

Especially the last two questions.

Reply 251

Jm098

see like that's a string question in a vertical circle in jan 12

This is my 6)b)

Original post by maisym00

What is the correct answer

correct answer is

\frac{1-2\mu^2}{4\mu}

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Reply 254

rainbowtwist

Anyone else get this for the separation of variables question? (I think it was Q6b) ImageUploadedByStudent Room1467041052.503698.jpg

Reply 255

rainbowtwist

Original post by jjsnyder

correct answer is

\frac{1-2\mu^2}{4\mu}

Posted from TSR Mobile

Where does the mu^2 come from? I didn't see any reason to square mu :/

Reply 256

Pentaquark

How many marks would i lose :s (7 marker)
I've got my friction on the wall the wrong way up hence
2u^2 +1 /4u not 1-2u^2/4

(edited 7 years ago)

Reply 257

rainbowtwist

Should the two frictions act upwards and to the left on the moments question?

Reply 258

Pentaquark

Original post by rainbowtwist

Should the two frictions act upwards and to the left on the moments question?

I've got my friction from the wall the wrong way up lol
The friction from the ground acts left as the ladder wants to slide down so the friction opposes that.
The friction from the wall, since the ladder wants to slide down the friction should be pointing upwards hence why my answer + not -. ffs :angry:

I'm dropping marks everywhere :frown:

Reply 259

RDKGames

Study Forum Helper

I DIDN'T DO THE ENERGY LOST BY FRICTION CORRECTLY!!! FUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUU.....................

Couldn't get an answer for the ladder one either but showed some working out on moments and resolving forces... just gonna casually slip away from this thread, not even 24 hours passed and I'm already dreading it by looking here xD