Given that p = 2i – 5j and q = i – 3j, find the unit vector in the direction of 3p – 4q.
- (a)Given that p = 2i – 5j and q = i – 3j, find the unit vector in the direction of 3p – 4q.[4]
- (b)A river flows between parallel banks at a speed of 1.25kmh⁻¹. A boy standing at point A on one bank sends a toy boat across the river to his father standing directly opposite at point B. The toy boat, which can travel at vkmh⁻¹ in still water, crosses the river with resultant speed 2.73 kmh⁻¹ along the line AB. [Figure 8.1]
- (b)(i)Calculate the value of v.[2]
- (b)(ii)The direction in which the boy points the boat makes an angle θ with the line AB. Find the value of θ.[2]
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Mark scheme
Marking points from the official mark scheme (May/June 2018). The mark or mark type is shown in brackets.
- [M1] For expansion and collection of terms
- [A1] 2i-3j
- [M1] For method to find magnitude
- [A1] (2i-3j)/√13
- [B1] Correct use of Pythagoras
- [B1] v = 3.00
- [M1] Use of a trig funtion to obtain a relevant angle
- [A1] Angle to AB=24.6° or 0.429 radians
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