NSAA Help with physics and maths questions

Original post by AspiringUnderdog

wow I just realised that I got this wrong because when rationalising I made 8 x1/sqrt2 8sqrt2 when it should be 4sqrt2. Thanks though!

for 85:

perpendicular lines so product of gradients = -1 ----> m=-1/p (1)

distance between intersection of lines with x axis = 5 ----> -2/p + 3/m =5 (2)

Solving simultaneously by subbing (1) in (2) gives a quadratic in p:

3p^2 +5p +2 = 0 solving this gives p= -1 or p= -2/3

But m cannot be 1 so p cannot be -1 as m= -1/p

Therefore p = -2/3 and m= 3/2 and m+p = 5/6

Reply 61

Anonymouspsych

16

Btw @AspiringUnderdog I have applied for Engineering at Cambridge so I will sit the ENGAA on 2nd Nov which has the same maths and physics section as NSAA for the first section I think haha but second section is different for ENGAA and NSAA

Reply 62

ImprobableCacti

15

Original post by AspiringUnderdog

Also could you try 85 please.

I'll try help you understand anything you still don't get tomorrow :smile:

Reply 63

ChallengeLover

14

Original post by Anonymouspsych

85 I got D

I got 88 to be D but I don't even get the question how can two horizontal forces be right angles to each other??? surely they are parallel

I think that when it says horizontal here it means that they are acting in the horizontal plane so go across the surface instead of perpendicular to the plane itself.

Since the forces act perpendicular, the resultant of them OS the hypotenuse of the right angled triangle so we get sqrt(9^2+12^2)=15N.
Friction=coeff(of friction)*mg=0.25*2*10=5N.
Resultant of these two forces is 15N-5N=10N since they act in a straight line in opposing directions.
F=ma
a=10/2=5.

Reply 64

AspiringUnderdog

OP

21

Original post by Anonymouspsych

for 85:

perpendicular lines so product of gradients = -1 ----> m=-1/p (1)

distance between intersection of lines with x axis = 5 ----> -2/p + 3/m =5 (2)

Solving simultaneously by subbing (1) in (2) gives a quadratic in p:

3p^2 +5p +2 = 0 solving this gives p= -1 or p= -2/3

But m cannot be 1 so p cannot be -1 as m= -1/p

Therefore p = -2/3 and m= 3/2 and m+p = 5/6

Original post by Anonymouspsych

Btw @AspiringUnderdog I have applied for Engineering at Cambridge so I will sit the ENGAA on 2nd Nov which has the same maths and physics section as NSAA for the first section I think haha but second section is different for ENGAA and NSAA

Ah right that makes sense. I made some stupid mistakes. made m =-p instead of -1/p. I tried making both equations equal to each other but it got a different answer why do you think that that is?

Also, good luck for that. We'll probably get similar questions for Section 1 but not section 2. Probably is still worth trying NSAA questions from section 2 for practise and vice versa for me.