Example 1 · level 1
A stone dropped from rest from a tall tower hits the ground after 2 s. With what speed (in m/s) does it hit the ground? Take g = 10 m/s² and ignore air resistance.
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- v = 10 × 2 = 20 m/s.
Answer: 20
CLASS 9 SCIENCE · GRAVITATION
Free fall under gravity
A freely falling body has acceleration g (take 10 m/s² unless told otherwise). Use v = gt, h = ½gt², v² = 2gh for a body dropped from rest.
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Worked examples
Example 2 · level 2
A stone dropped from a bridge in Surat reaches the water in 2 s. Find the height of the bridge above the water (in m). Take g = 10 m/s².
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- h = ½ × 10 × 4 = 20 m.
Answer: 20 m
Example 3 · level 3
A ball is thrown straight up at 50 m/s. Find the maximum height it reaches (in m). Take g = 10 m/s².
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- 0 = 50² − 2 × 10 × h
- h = 2500 ÷ 20 = 125 m.
Answer: 125 m