Question

A fire cracker is fired and it rises to a height of 1000 m. Find the velocity by which it was

released and the time taken by it to reach the highest point (take a = 10 m/s²). step by step​

Answer 1

Explanation:

v=100√2m/s

t=10√2s

hope you will understand.

Answer 2

Gɪᴠᴇɴ :-

• Distance travelled (h) = 1000m
• Final velocity (v) = 0 m/s --(At rest)
• Acceleration due to gravity (g) = -10 m/s²

ᴛᴏ ғɪɴᴅ :-

• Initial velocity (u)
• Time taken (t)

sᴏʟᴜᴛɪᴏɴ :-

On using 3rd equation of free falling motion , we get,

➦ v² - u² = 2gh

➮ (0)² - (u) ² = 2 × -10 × 1000

➮ -u² = -20000

➮ u² = 20000

➮ u = √20000

➮ u = 100√2 m/s

Hence,

• Initial velocity is 100√2 or 141 m/s

Now,

On using 1st equation of free falling motion, we get,

➦ v = u + gt

➮ 0 = 100√2 + -10×t

➮ 10t = 100√2

➮ t = 100√2/10

➮ t = 10√2 s

➮ t = 10 × 1.41 = 14.1 ≈ 14 seconds

Hence,

• Time taken (t) is 14 seconds.

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NOTE :-

• Real value of acceleration due to gravity (g) is 9.8 m/s² but to make calculation easier we use g = 10 m/s² .

• In this question we took g = -10 m/s² because the rocket is going in opposite direction of gravity.

• Use √2 = 1.41

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