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WAEC Further Mathematics 2007 Question 34

Question 34

Dynamics

A particle is projected vertically upwards with a speed of 40 ms−1. At what times will it be 35m above its point of projection? [Take g = 10ms−2]

  1. A.1 sec. and 7 sec.
  2. B.1 sec. and 8 sec.
  3. C.2 sec. and 5 sec.
  4. D.2 sec. and 7sec.
Show the answer and explanation

Answer: A (1 sec. and 7 sec.)

Explanation

35 = 40t − 5t², so t² − 8t + 7 = 0, (t − 1)(t − 7) = 0: at 1 s (going up) and 7 s (coming down).