The diagram shows a solid cylinder standing on a horizontal circular base with centre O and radius 4 units. Points A, B and C lie on the circumference of the base such that AB is a diameter and angle BOC = 90°. Points P, Q and R lie on the upper surface of the cylinder vertically above A, B and C respectively. The height of the cylinder is 12 units. The mid-point of CR is M and N lies on BQ with BN = 4 units. Unit vectors i and j are parallel to OB and OC respectively and the unit vector k is vertically upwards. Evaluate PN.PM and hence find angle MPN.
- (a)Evaluate PN ⋅ PM and hence find angle MPN.[7]
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- [B1] PN = 8i - 8k
- [B2,1,0] PM = 4i + 4j – 6k
- [M1] PN.PM = 32 + 0 + 48 = 80
- [M1] |PN| × |PM|= √128 × √68
- [M1] √128 × √68 cos MPN = 80
- [A1] Angle MPN = 31.0° awrt
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