Processing math: 100%

Vector (Velocity/ Position/ Speed)

(CIE 0606/2021/m/12/Q5)
In this question all lengths are in kilometres and time is in hours. Boat A sails, with constant velocity, from a point O with position vector (00). After 3 hours A is at the

point with position vector (129.)

(a) Find the position vector, OP, of A at time t. [1]

At the same time as A sails from O, boat B sails from a point with position vector (126), with constant velocity (58).

(b) Find the position vector, OQ, of B at time t. [1] 

(c) Show that at time t,|PQ|2=26t2+36t+180.  [3] 

(d) Hence show that A and B do not collide. [2]

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*********math solution*************
(a) Let v=(v1v2) be velocity vector. 
After t hours, the position vector of P is
OP=(00)+t(v1v2)
At t=3

 (129)=(00)+3(v1v2)=(3v13v2)v1=4,v2=3OP=(00)+t(43)=(4t3t) (b) ¯OQ=(126)+t(58)=(125t6+8t) (c) PQ=¯OQ¯OP=(125t6+8t)(4t3t)=(12t6+5t)

|PQ|2=(12t)2+(6+5t)2=(14424t+t2)+(36+60t+25t2)=26t2+36t+180(d)  Conrider 26t2+36t+180=0 Discriminant =b24ac=3624×26×180=17424<0 Thus the equation has no solution. |PQ|0 for any t. Hence A and B do not collide. 

**********end math solution********************

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