NCERT Solutions for Class 9 Science Chapter 8
Motion
NCERT Books for Session 2022-2023
CBSE Board and UP Board
Intext Questions
Page No-110
Questions No-5
A stone is thrown in a vertically upward direction with a velocity of 5 m s-1. If the acceleration of the stone during its motion is 10 m s–2 in the downward direction, what will be the height attained by the stone and how much time will it take to reach there?
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Here we have,
Initial velocity (u) = 5 m/s
Final velocity (v) = 0 m/s
Acceleration (a) = – 10 m/s²
Height, i.e. Distance, s =?
Time (t) taken to reach the height =?
We know that, v² = u² + 2as
⇒ 0 = (5) ² + 2 × −10 × s
⇒ 0 = 25 − 20s
⇒ s = 25/20 m
⇒ s = 1.25 m
Now, we know that, v = u + at
⇒ 0 = 5 + (–10) × t
⇒ 0 = 5 − 10t
⇒ t = 5/10 s
⇒ t = 0.5 s
Thus, stone will attain a height of 1.25 m and time taken to attain the height is
0.5 s.
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