Lesson eLearning

A ball is thrown vertically upward from the ground with an initial speed of 30 m/s. Taking the acceleration due to gravity as 10 m/s², after how many seconds will its speed become 10 m/s on its way down?

hard MCQ 4 marks Class 9 · Science · Motion
  1. a) 3 s
  2. b) 4 s
  3. c) 5 s
  4. d) 6 s
Answer
b) 4 s

The correct answer is b) 4 s — Thus the ball reaches a speed of 10 m/s downward after 4 s

Step-by-step solution

  1. Use v = u – g t, where v is final speed, u is initial speed, g = 10 m/s²
  2. Set v = –10 m/s (negative because downward)
  3. –10 = 30 – 10 t → 10 t = 40 → t = 4 s
  4. Thus the ball reaches a speed of 10 m/s downward after 4 s
Common mistake: ignoring sign of velocity or using v = u + gt

Concept tested: vertical motion kinematics

Published · How this solution was prepared and checked

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