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Add math past paper question

rahul03

I'm unable to solve this question from cie add math past paper. please explain how to arrive at correct answer.

image(2).jpeg397.2KB

Reply 1

TeeEm

Original post by rahul03

I'm unable to solve this question from cie add math past paper. please explain how to arrive at correct answer.

draw a velocity diagram

then sine rule

Reply 2

rahul03

Original post by TeeEm

draw a velocity diagram

then sine rule

Hi TeeEm,

Thanks for replying.

I have drawn the velocity diagram.

(In the diagram i wrote resultant force instead of resultant velocity).
But how do i apply the sin rule? the angle between the vectors is not given.

thanks again,

rahul

(edited 9 years ago)

diagram for velocity.png3.5KB

Reply 3

interstitial

Original post by rahul03

Hi TeeEm,

Thanks for replying.

I have drawn the velocity diagram.

(In the diagram i wrote resultant force instead of resultant velocity).
But how do i apply the sin rule? the angle between the vectors is not given.

thanks again,

rahul

think about what it means for something to be north east...

Reply 4

TeeEm

Original post by rahul03

Hi TeeEm,

Thanks for replying.

I have drawn the velocity diagram.

But how do i apply the sin rule? the angle between the vectors is not given.

thanks again,

rahul

_wV_c=V_w-V_c

c=cyclist, w=wind

first rearrange to

V_w=_wV_c+V_c

then ...

Reply 5

TeeEm

draw velocity of cyclist "down"
velocity of wind relative to cyclist at bearing 225, since it is coming from NE

can you take it from there?

your diagram does not make sense to me

Reply 6

rahul03

Original post by TeeEm

draw velocity of cyclist "down"
velocity of wind relative to cyclist at bearing 225, since it is coming from NE

can you take it from there?

your diagram does not make sense to me

Yes, thanks. Now i can solve it. thanks a lot for helping me :smile:

pleasure

Original post by rahul03

I'm unable to solve this question from cie add math past paper. please explain how to arrive at correct answer.

Ok start off by focusing whats relative to what. E.g. the wind is relative to the cyclist. this is how the cyclist 'Sees the wind'. We write that as wVc and this is derived as wVc=Vw-Vc.

Then by drawing the triangle make sure it matches so that the cyclist (-Vc) is now shown traveling in a north direction. The triangle should give one of the angles as 135* degrees... And with the velocity of wind given and velocity of cyclist given, it should be easy to see the sine rule needed to find the angle of Vw. I ended up getting S(20.64*)W OR W(69.36*)S.