Question

Question : A vehicle is having the retardation of 6ms -2 when it applies brakes & came to rest after 5 sec. What is the initial velocity of the body ?​

Answer 1

Correct option is
A
15ms
−1

Time, t=3s
Retadation, a=5m/s
2

Final velocity, v=0
Intial velocity, =u
So, v=u−at
0=u−5×3
u=15 ms
−1
Do like same
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Answer 2

Answer :

• Initial velocity of the vehicle is 30 m/s.

Explication of steps :

Here, we are given that,

» Retardation = 6 m/s²

If retardation is 6 m/s², so acceleration (a) is -6 m/s².

» Final velocity (v) = 0 m/s

[Since, it came to rest.]

» Time taken (t) = 5 sec

We have to find the initial velocity (u) of the vehicle.

By using the first equation of motion,

★ v = u + at

• v denotes final velocity
• u denotes initial velocity
• a denotes acceleration
• t denotes time taken

Substituting values in the above formula to find initial velocity of the the vehicle.

→ 0 = u + [(-6) × 5]

→ 0 = u + (-30)

→ 0 = u - 30

→ 0 + 30 = u

→ 30 = u

Therefore, initial velocity of the vehicle is 30 m/s.

______________________________

⠀⠀⠀⠀⠀⠀⠀⠀Know More!

First equation of motion :

• v = u + at

Second equation of motion :

• s = ut + $\sf \dfrac{1}{2} at^2$

Third equation of motion :

• v² - u² = 2as

Here,

• v denotes final velocity
• u denotes initial velocity
• a denotes acceleration
• t denotes time
• s denotes distance

» When the body starts from rest, its initial velocity is 0.

» When the body applies break and comes to rest, its final velocity is 0.