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WAEC Further Mathematics 2010 Question 31

Question 31

Vectors

Two particles are fired together along a smooth horizontal surface with velocities 4ms−1 and 5ms−1. If they move at 60° to each other, find the distance between them after 2 seconds.

  1. A.2√61
  2. B.2√41
  3. C.2√21
  4. D.2√10
Show the answer and explanation

Answer: C (2√21)

Explanation

After 2 s they are 8 m and 10 m from the start. By the cosine rule d2 = 64 + 100 − 2(8)(10)cos 60° = 84, so d = √84 = 2√21 m.