In this question \mathbf{i} is a unit vector due East and \mathbf{j} is a unit vector due North. At 12 00 hours, a ship leaves a port P and travels with a speed of 26 kmh⁻¹ in the direction 5\mathbf{i} + 12\mathbf{j}.
- (i)Show that the velocity of the ship is (10\mathbf{i} + 24\mathbf{j}) kmh⁻¹.[2]
- (ii)Write down the position vector of the ship, relative to P, at 16 00 hours.[1]
- (iii)Find the position vector of the ship, relative to P, t hours after 16 00 hours.[2]
- (iv)At 16 00 hours, a speedboat leaves a lighthouse which has position vector (120\mathbf{i} + 81\mathbf{j}) km, relative to P, to intercept the ship. The speedboat has a velocity of (-22\mathbf{i} + 30\mathbf{j}) kmh⁻¹. Find the position vector, relative to P, of the speedboat t hours after 16 00 hours.[1]
- (v)Find the time at which the speedboat intercepts the ship and the position vector, relative to P, of the point of interception.[4]
Mark scheme
Marking points from the official mark scheme (May/June 2014). The mark or mark type is shown in brackets.
- [M1] (i) M1 for 26/13 (5i+12j)
- [A1] (i) A1
- [M1] (i) M1 for working from given answer to obtain the given speed
- [A1] (i) A1 for a completely correct method
- [M1] (i) M1 for attempt to obtain the 'multiple' and apply to the direction vector
- [A1] (i) A1 for a completely correct method
- [M1] (i) M1 for reaching this stage
- [A1] (i) A1 for a completely correct method
- [B1] (ii) B1 Allow either form for B1
- [M1] (iii) M1 for their (ii) + (10i + 24j)t or (10i + 24j)×(t + 4)
- [A1] (iii) A1 correct answer only
- [B1] (iv) B1
- [M1] (v) M1 for equating like vectors
- [A1] (v) A1 Allow for t = 2.5
- [DM1] (v) DM1 for use of t to obtain position vector
- [A1] (v) A1 cao
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