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# Edexcel M1 - Vectors Watch

1. I'm having problems with this question

A small boat S, drifting in the sea, is modelled as a particle moving in a straight line at constant speed. When first sighted at 0900, S is at a point with position vector (-2i-4j)km relative to a fixed origin O, where i and j are unit vectors due east and due north respectively. At 0940, S is at the point with position vector (4i-6j)km. At time t hours after 0900, S is at the point with position vector skm.

a) Calculate the bearing on which S is drifting.
b) Find an expression for s in terms of t.
at 1100 a motor boat M leaves O and travels with constant velocity (pi + qj)kmh-1
c) Given that M intercepts S at 1130, calculate the value of p and the value of q

I managed to find a) which is 108degrees. For the b) part, don't I need the velocity of S to apply the formula of r=r0+vt?

Also, to find c) I need to get the equation at b) first right?
2. (Original post by Akiraryuu)
I'm having problems with this question

A small boat S, drifting in the sea, is modelled as a particle moving in a straight line at constant speed. When first sighted at 0900, S is at a point with position vector (-2i-4j)km relative to a fixed origin O, where i and j are unit vectors due east and due north respectively. At 0940, S is at the point with position vector (4i-6j)km. At time t hours after 0900, S is at the point with position vector skm.

a) Calculate the bearing on which S is drifting.
b) Find an expression for s in terms of t.
at 1100 a motor boat M leaves O and travels with constant velocity (pi + qj)kmh-1
c) Given that M intercepts S at 1130, calculate the value of p and the value of q

I managed to find a) which is 108degrees. For the b) part, don't I need the velocity of S to apply the formula of r=r0+vt?

Also, to find c) I need to get the equation at b) first right?
For part (b) you need to use r=r0+vt, and you need to sub in the velocity which you found in part (a).
3. (Original post by raheem94)
For part (b) you need to use r=r0+vt, and you need to sub in the velocity which you found in part (a).
Isn't part a) asking for the bearing? I don't see any velocity equation there
4. (Original post by Akiraryuu)
Isn't part a) asking for the bearing? I don't see any velocity equation there
Yes, part (a) is asking for the bearing. There will be alternative techniques to do part (a) but the way i did that required to find the velocity vector.

Just find the velocity vector and do part (b).
5. (Original post by raheem94)
Yes, part (a) is asking for the bearing. There will be alternative techniques to do part (a) but the way i did that required to find the velocity vector.

Just find the velocity vector and do part (b).
Oh! I solved part a) using trig. That's the problem, I have no idea how to get the velocity vector from the two position vector equations.
6. (Original post by Akiraryuu)
Oh! I solved part a) using trig. That's the problem, I have no idea how to get the velocity vector from the two position vector equations.
You know the formula,

We know that

We know that at 0940(which is t=2/3 if we measure time in hours)

So using the formula, , we get,
7. (Original post by raheem94)
You know the formula,

We know that

We know that at 0940(which is t=2/3 if we measure time in hours)

So using the formula, , we get,
Oh god, why didn't I see the connection sooner? Gah. Thank you so so so much.
8. (Original post by Akiraryuu)
Oh god, why didn't I see the connection sooner? Gah. Thank you so so so much.
No problem.

Do you know how to do part (c)?
9. (Original post by raheem94)
No problem.

Do you know how to do part (c)?
Yep, got it. My only problem was finding the vector equation. Thanks again.
10. how do we find the time ?
11. A boat B is moving with constant velocity. At noon, B is at the point with position vector
(3i – 4j) km with respect to a fixed origin O. At 1430 on the same day, B is at the point
with position vector (8i + 11j) km.
(a) Find the velocity of B, giving your answer in the form pi + qj.

how to find the time im stuck in this
12. (Original post by sowmyaraju)
A boat B is moving with constant velocity. At noon, B is at the point with position vector
(3i – 4j) km with respect to a fixed origin O. At 1430 on the same day, B is at the point
with position vector (8i + 11j) km.
(a) Find the velocity of B, giving your answer in the form pi + qj.

how to find the time im stuck in this
i think you need to use r=Ro+vt
so (8i+11j)=(3i-4j) + 2.5v
(8i+11j) - (3i - 4j) =2.5v
(5i + 15j) = 2.5v
v= 2i + 6j
13. What does it mean when something says find the time when X is moving 'due east of something'

equate the i components?
14. (Original post by Obscenedilemma)
What does it mean when something says find the time when X is moving 'due east of something'

equate the i components?
If X moves due east of Y then the j components of both are same, so equate the j components.
15. hey......can sm1 hlp me wid dis question
given that a=2i+5j and b=3i-j find X if a+Xb is parallel to vector i
16. (Original post by backstreet1)
hey......can sm1 hlp me wid dis question
You need to start a thread not add to an old one

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