Question

A moving train is brought to rest within 20 s by applying brakes find the initial velocity if the retardation due to brakes is 2 m/s²​

Answer 1

$\underline{\orange{\bf Given :-}}$

• Final Velocity(v) = 0 m/s
• Time(t) = 20 sec
• Acceleration(a) = - 2 m/s²

$\underline{\orange{\bf To \: Find :-}}$

• Initial Velocity

$\underline{\orange{\bf Solution :-}}$

☆ As we know that ☆

$\: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \:$$\large\boxed{\sf v = u + at}$

☆ Where ☆

• v = Final Velocity
• u = Initial Velocity
• a = Acceleration
• t = Time

☆ Putting all values we get ☆

$\implies$0 = u + (− 2) × 20

$\implies$0 = u − 40

$\implies$$\cancel{-}$u = $\cancel{-}$40

$\implies$u = 40 m/s

Therefore, Initial Velocity is 40 m/s

Answer 2

Given :-

☄ Final Velocity of the train, v = 0 m/s

☄ Time taken, t = 20 sec

☄ accerlation of the train, a = - 2 m/s²

|| Note :- the negative accerlation is called retardation ||

To Find :-

Initial Velocity of train

Solution :-

as we are provided with constant accerlation, final velocity and time we can use equation of motion

so, using equation of motion .i.e.,

➠ v = u + at

here,

v denotes Final Velocity, u denotes Initial Velocity, a denotes acceleration and t denotes Time

➠ 0 = u + (− 2)(20)

➠ 0 = u − 40

➠ u = 40 m/s

thus, the Initial Velocity of the train is 40 m/s

$⠀⠀⠀⠀$

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