Question

A ball is gently dropped from a height of 20 m. if its velocity increases uniformly at the rate of 10 metre per second square, with what velocity will it strike the ground? after what time will it strike the ground?

Answer 1

Given,
Distance (s) = 20 m
Accelaration (a) = 10 m/s²
Initial Velocity (u) = 0 m/s
Final velocity (v) = ?
Time (t) = ?

We know,
v² - u² = 2as
v² - 0 = 2 * 10 * 20
v² = 400
v = √400
v = 20 m/s

And, 

v = u+at
20 = 0 + 10 * t
20 = 10 t
t = 2 second

∴ Striking velocity = 20 m/s
∴ Striking time = 2 second

Answer 2

ɢɪᴠᴇɴ

ɪɴɪᴛɪᴀʟ ᴠᴇʟᴏᴄɪᴛʏ(ᴜ) = 0 ᴍ/ꜱ

ᴀᴄᴄᴇʟᴇʀᴀᴛɪᴏɴ (ᴀ) = 10 ᴍ/ꜱ²

ᴛɪᴍᴇ(ꜱ) = 20 ᴍ

ᴡᴇ ᴋɴᴏᴡ

ᴠ² = ᴜ² + 2ᴀꜱ

ᴘᴜᴛᴛɪɴɢ ᴠᴀʟᴜᴇꜱ:

ᴠ² = 0² + 2 (10 x 20)

ᴠ² = 400

ᴠ = 20 ᴍ/ꜱ

ꜰᴏʀ ᴛɪᴍᴇ:

ᴠ = ᴜ + ᴀᴛ

ᴛ = ᴠ - ᴜ/ᴀ

ᴛ = (20-0)10

  = 20/10

  = 2

∴ ꜱᴛʀɪᴋɪɴɢ ᴠᴇʟᴏᴄɪᴛʏ = 20 ᴍ/ꜱ

∴ ꜱᴛʀɪᴋɪɴɢ ᴛɪᴍᴇ = 2 ꜱᴇᴄᴏɴᴅꜱ