Question

A cricket ball is dropped from the height of 20 m . Calculate the speed of the ball when it hits the ground and calculate the time it takes to fall through this height.

Answer 1

by using 3rd eqn of motion,
cosider g as 10m/s^2 approx to 9.8 m/s^2

v^2 = u^2+2gs (when we drop or release any object its initial velocity is always zero)
v^2 = 0+2(10)(20)
v^2 = 400
v = 20m/s

by using 1st eqn of motion, we will find time
v = u+gt
20 = 0+10(t)
10t = 20
t = 2sec

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Answer 2

Aɴsᴡᴇʀ:

• The speed of ball when it hits the ground = 20 m/s
• The time it takes to fall through this height = 2 seconds

Gɪᴠᴇɴ

• The given height is 20 m.
• Initial Velocity is 0 m/s.
• Acceleration due to gravity is 10 N.

Nᴇᴇᴅ Tᴏ Fɪɴᴅ:

• The speed of ball when it hits the ground = ?
• The time it takes to fall through this height = ?

Solution:

♲︎︎︎In case 1:

• The speed of ball when it hits the ground = ?

Fᴏʀᴍᴜʟᴀ ᴜsᴇᴅ ʜᴇʀᴇ:

• v² - u² = 2gh

Pᴜᴛᴛɪɴɢ ᴛʜᴇ ᴠᴀʟᴜᴇs:

➦ v² - 0² = 2 × 10 × 20

➦ v² = 400

➦ velocity = √200

➦ velocity = 20 m/s

Tʜᴇʀᴇғᴏʀᴇ:

• The speed of ball when it hits the ground is 20 m/s.

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♲︎︎︎In case 2:

• The time it takes to fall through this height = ?

Fᴏʀᴍᴜʟᴀ ᴜsᴇᴅ ʜᴇʀᴇ:

• v = u + gt

Pᴜᴛᴛɪɴɢ ᴛʜᴇ ᴠᴀʟᴜᴇs:

➦ 20 = 0 + 10 × t

➦ 20 = 10t

➦ 10t = 20

➦ Time = 20/10

➦ Time = 2 sec

Tʜᴇʀᴇғᴏʀᴇ:

• The time it takes to fall through this height is 2 seconds.

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