Question

A car is moving in a straight line with speed 18km/h. It is stopped in 10 s by applying the brakes. Find the retardation. 

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Answer 1

Given :-

• Initial velocity of car = 18 km/h
• Stopped by applying brakes in 10s

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We need to find :-

• Retardation = ?

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Solution :-

Finding acceleration using ,

a = v - u/t

Where ,

• u → initial velocity = 18 km/h = 5m/s
• v → final velocity = 0 km/h = 0 m/s
• a → acceleration = ?
• t → time taken = 10s

Note :- Here the final velocity of the car will be zero , because the car is stopped by applying brakes.

Substituting the values we have ,

→ a = 0 - 5/10

→ a = - 5/10

→ a = - 0.5 m/s²

Note :- Negative sign shows retardation .

Hence , retardation of the car is -0.5 m/s²

Answer 2

GIVEN :-

• A ᴄᴀʀ ᴍᴏᴠɪɴɢ ɪɴ ᴀ sᴛʀᴀɪɢʜᴛ ʟɪɴᴇ ᴡɪᴛʜ sᴘᴇᴇᴅ 18 ᴋᴍ/h .

• Iᴛ ɪs sᴛᴏᴘᴘᴇᴅ ɪɴ 10 s ʙʏ ᴀᴘᴘʟɪɴɢ ᴛʜᴇ ʙʀᴀᴋᴇs .

TO FIND :-

• Tʜᴇ ʀᴇᴛᴀʀᴅᴀᴛɪᴏɴ .

SOLUTION :-

$\huge\orange\star$ $\bf\pink{v\:=\:u\:+\:at\:}$

Wʜᴇʀᴇ,

• ᴠ = ғɪɴᴀʟ ᴠᴇʟᴏᴄɪᴛʏ

• ᴜ = ɪɴɪᴛɪᴀʟ ᴠᴇʟᴏᴄɪᴛʏ

• a = ᴀᴄᴄᴇʟᴇʀᴀᴛɪᴏɴ

• t = ᴛɪᴍᴇ

According to the question,

☯︎ ᴛʜᴇ ᴄᴀʀ ᴡᴀs ᴀᴘᴘʟʏɪɴɢ ʙʀᴀᴋᴇs, sᴏ ᴀғᴛᴇʀ sᴏᴍᴇᴛɪᴍᴇ ᴛʜᴇ ᴄᴀʀ ɪs sᴛᴏᴘᴘᴇᴅ .

• Sᴏ, ᴠ = 0 m/s

• ᴜ = 18 ᴋᴍ/h = 18 × 5/18 = 5 m/s

• a = ?

• t = 10 s

⟼ 0 = 5 + (a × 10)

➟ a × 10 = -5

➟ a = -5/10

➟ a = -1/2

➟ a = -0.5 m/s²

[Note :- Here, retardation is occured . So, acceleration results -ve .]

$\huge\bf\red{\therefore}$ Tʜᴇ ʀᴇᴛᴀʀᴅᴀᴛɪᴏɴ ᴏғ ᴛʜᴇ ᴄᴀʀ ɪs "-0.5ᴍ/s²" .