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JAMB Physics 1997 Question 7

Question 7

Newton's Laws and Momentum

A body of mass 2 kg moving vertically upwards has its velocity increased uniformly from 10 m s−1 to 40 m s−1 in 4 s. Neglecting air resistance, calculate the upward vertical force acting on the body. [g = 10 m s−2]

  1. A.15 N
  2. B.20 N
  3. C.35 N
  4. D.45 N
Show the answer and explanation

Answer: C (35 N)

Explanation

a = (40 − 10)/4 = 7.5 m s−2. The force must hold up the weight and also accelerate it: F = m(g + a) = 2 × 17.5 = 35 N.