(c) Find the total time for the coin to return to the end of the slope. [7 marks]
Using Newton's second law, and the same method as part (a), but noting the friction now acts up the slope, we get a = g(sin 30 - 0.2 cos 30) = 3.20 ms^-2
On the way up, v=u+at⇒t=av−u=−6.600−4=0.606s
On the way down, s=ut+21at2⇒1.21=21×3.20×t2⇒t=21×3.201.21=0.870s
So the overall time is 1.48 s.
Q8 (I'll update this later)
(a) Find the time for the particles to collide. [5 marks]
How did people do the bearing question? Couldn't find any angles other than 50•?! Also what pet of mechanics was the coin question? Didn't have any mass so couldn't do any of it- that's 14 marks down the drain ):
I don't agree on the bearing question... I used the cosine rule to get a resultant velocity of 133.7 and then the cosine rule again to find the angle within that triangle which was 7 degrees, then added the original 40 on to get a final bearing of 047 (I know a lot of others did this too)
How did people do the bearing question? Couldn't find any angles other than 50•?! Also what pet of mechanics was the coin question? Didn't have any mass so couldn't do any of it- that's 14 marks down the drain ):
Mass cancelled out as Sum of Forces = -(mu)mgcos30 -mgsin30 = ma
I don't agree on the bearing question... I used the cosine rule to get a velocity of 133.7 and then the cosine rule again to find the angle within that triangle which was 7 degrees, then added the original 40 on to get a final bearing of 047 (I know a lot of others did this too)
It is 108 and 32 degrees because we were given the actual velocity this time and we had to find V which was the velocity relative to the air basically the reverse of what questions have been like on most past paper questions. Velocity relative to air = vel of plane - vel of air so if you draw a vector diagram of that alpha has to be less than 40 degrees.
I don't agree on the bearing question... I used the cosine rule to get a resultant velocity of 133.7 and then the cosine rule again to find the angle within that triangle which was 7 degrees, then added the original 40 on to get a final bearing of 047 (I know a lot of others did this too)
It is 108 and 32 degrees because we were given the actual velocity this time and we had to find V which was the velocity relative to the air basically the reverse of what questions have been like on most past paper questions.
got about 4 marks in that paper no word of a lie and no exaggeration like honestly 4 marks u probably think im joking but mums life.... how many ums is that?
Did anyone find the paper way harder than last year? I practised the 2017 paper yesterday and got 90 UMS. But i flopped today's paper big times 😭 Any grade boundary predictions for this paper?