A coastguard station receives a distress call from a ship which is travelling at 15 kmh⁻¹ on a bearing of 150°. A lifeboat leaves the coastguard station at 1500 hours; at this time the ship is at a distance of 30 km on a bearing of 270°. The lifeboat travels in a straight line at constant speed and reaches the ship at 1540 hours.
- (i)Find the speed of the lifeboat.[5]
- (ii)Find the bearing on which the lifeboat travelled.[3]
Mark scheme
Marking points from the official mark scheme (May/June 2011). The mark or mark type is shown in brackets.
- [1] (i) Diagram with 60° (or similar vector resolution)
- [1] (i) 10 (km distance by ship) or 45 (km distance for alternative method)
- [1] (i) Uses cosine rule
- [1] (i) D² = 10² + 30² – 2 × 10 × 30 × cos60 or V² = 15² + 45² – 2 × 15 × 45 × cos60
- [1] (i) 39.7 or 39.8 or 15√7
- [1] (ii) sinα/10 = sin60/(10√7) (or sinβ/30 = sin60/(10√7) and use β)
- [1] (ii) α = 19.1 or β = 101
- [1] (ii) 251
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