Answer only one of the following two alternatives. EITHER At 1200 hours, a ship has position vector (54i + 16j) km relative to a lighthouse, where i is a unit vector due East and j is a unit vector due North. The ship is travelling with a speed of 20km h⁻¹ in the direction 3i +4j.
- (i)Express OQ and PQ in terms of a and b.[2]
- (ii)Express QR in terms of λ, a and b.[2]
- (iii)Express QR in terms of μ, a and b.[3]
- (iv)Hence find the value of λ and of μ.[3]
This question uses a diagram from the original paper, which isn't shown here. Open the full paper from the past papers archive to see it.
Mark scheme
Marking points from the official mark scheme (May/June 2012). The mark or mark type is shown in brackets.
- [B1] Allow unsimplified
- [B1] Follow through on their OQ, allow unsimplified
- [M1] M1 for λa – their OQ
- [A1] A1 - allow unsimplified
- [M1] M1 for attempt to obtain QR in terms of PQ
- [M1] M1 for attempt to simplifiy
- [A1] QR = (μ/(1-μ))( (2/3)a - (11/12)b )
- [M1] M1 for equating like vectors and attempt to solve
- [A1] A1 for each
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