Rollercoaster Q WTF? (1 Viewer)

[boxhunter91]

Seriously dropped 4 marks from that crap.
No idea how to do it.
I got b=3.
Obviously that is wrong.. Cuz i couldnt work out a...

 

[ayehann]

you had to use the equation given for the parabola... find its derivatie and sub in the values for the two 'smooth' points...
because u had to have the same gradients when the line turns into the parabola to have a smoth transition.
so when u got the derivative.. you'd get two simultaneous equations to solve for a and b.
i cant remeber what i got for b... i think it was 1.2

 

[raniaaa]

y= ax^2 + bx
y'(x)= 2ax + b

at point O(0,0)
y'(x) = b
m= 1.2 therefore b=1.2

at point P: m= -1.8, P(30,y)
y'(x) = 60a + 1.2
-1.8 = 60a + 1.2
a= -20

 

[Thecorey0]

Seriously dropped 4 marks from that crap.
No idea how to do it.
I got b=3.
Obviously that is wrong.. Cuz i couldnt work out a...

I got b=1.2, a =-1/20

 

[AnandDNA]

um i found y(dash) = 2ax+b

and did y(-) (0) = 1.2

2a(0)+b=1.2

b=1.2

and the other one is y(-) (30) as it is 30 m to the right

so -1.8=2a(30)+1.2

and then u get (a)

but idk see what other ppl say :S

 

[ayehann]

y= ax^2 + bx
y'(x)= 2ax + b

at point O(0,0)
y'(x) = b
m= 1.2 therefore b=1.2

at point P: m= -1.8, P(30,y)
y'(x) = 60a + 1.2
-1.8 = 60a + 1.2
a= -20

-1.8 = 60a + 1.2
-3 = 60 a
a = -3/60
therefore a = -1/20 not -20

 

[sydneyroosters]

Gradient of RO = 1.2, which passes through (0,0)

y = ax^2 + bx
dy/dx = 2ax + b

at x = 0, m = 1.2

therefore, 1.2 = 2(a)(0) + b
b = 1.2

Gradient of QP = -1.8, and P is (30, y)

at x = 30, m = -1.8

therefore, -1.8 = 2(a)(30) + 1.2
-3 = 60a
a = - 1/20

a = -1/20
b = 1.2

ii) Equation is now: y = (-1/20)x^2 + 1.2x

vertex X = -b/2a
= 12

sub that into equation, y = 7.2

thus, v(12, 7.2)

now the distance D = vertical height from vertex to x-axis + height from x axis to Y coordinate of P

We know that P(30, y), sub 30 into the equation and you get -9

therefore P(30, -9)

D = 7.2 + 9
= 16.2

 

[raniaaa]

-1.8 = 60a + 1.2
-3 = 60 a
a = -3/60
therefore a = -1/20 not -20

omg if i made that mistake in the exam i will cry

 

[TechnIx]

Woo! So happy I got that 100% right.

It looked tricky at first, but it was an easy question.

a = - 0.05
b = 1.2

d = 16.2

yippie!

 

[Cataclysm]

My heart sank when I saw b=1.2.. But then I remembered I turned it into 6/5 :')

I think I got full marks on that question then... If b=6/5, a=-1/20 And d = some stupid fraction.. I think like 9+36/5 or something ?_?

 

[raniaaa]

omggggg i did do it right!!! i remember making the denominators all 20! omg yayayayayayayayyaayay!

 

[Nelson.]

omg, i got it right....i attacked that question with no clue how to do it

 

[Aplus]

Gradient of RO = 1.2, which passes through (0,0)

y = ax^2 + bx
dy/dx = 2ax + b

at x = 0, m = 1.2

therefore, 1.2 = 2(a)(0) + b
b = 1.2

Gradient of QP = -1.8, and P is (30, y)

at x = 30, m = -1.8

therefore, -1.8 = 2(a)(30) + 1.2
-3 = 60a
a = - 1/20

a = -1/20
b = 1.2

ii) Equation is now: y = (-1/20)x^2 + 1.2x

vertex X = -b/2a
= 12

sub that into equation, y = 7.2

thus, v(12, 7.2)

now the distance D = vertical height from vertex to x-axis + height from x axis to Y coordinate of P

We know that P(30, y), sub 30 into the equation and you get -9

therefore P(30, -9)

D = 7.2 + 9
= 16.2

Yeah, I got that too

 

[shady145]

I got b=1.2, a =-1/20

haha the post above urs scared me... yea this is what i got

 

[heavenfalling]

Crap I only got b correct. My brain didn't realise then that x was 30 not the y value. :/

 

[bmn]

I thought I was going wrong with those numbers, but I guess I was right.

 

[Aquawhite]

Woo! So happy I got that 100% right.

It looked tricky at first, but it was an easy question.

a = - 0.05
b = 1.2

d = 16.2

yippie!

Damn ya Brad >_<. I left part ii) since I -b/2a didn't spring to mind straight away, I had other marks to pick up I think...

 

[HailSatan]

Fairly easy question really...

 

[absorber]

b=1.2
a=-1/20
d=16.2

Yeah it was a fun question, though I think it was one of those either do or don't get it things

 

[Melisoverschool]

-1.8 = 60a + 1.2
-3 = 60 a
a = -3/60
therefore a = -1/20 not -20

OMG!! i actually got this, b=1.2 and a= -1/20

didn't get the next part but hey..i'm stoked i got any of it lol