Question

A moving train is brought to rest within 15 seconds by applying brakes. Find the initial velocity, if
the retardation due to brakes is 3 m/s2.

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Answer 1

Answer: Initial velocity = 45 m/s

Explanation:

Let the initial velocity be 'u', final velocity be 'v', time be 't' and acceleration be 'a'.

Given that,

t = 15 s

v = 0            ( since train is brought to rest )

a = -3 m/s^2     ( since there is retardation)

We know that,

                      --> v = u + at

                      --> 0 = u + (-3)(15)

                      --> 0 = u - 45

                      --> u = 45

Therefore, the initial velocity is 45 m/s .

Answer 2

Answer :

Given -

• t = 15 s
• v = 0 m/s
• a = -3 m/s²

To Find -

• u = ?

Solution -

We know that, v = u + at.

Using it to find u,

⇒ 0 = u + (-3)(15)

⇒ u = 45 m/s

More Information -

• Displacement is a vector quantity.
• Distance is a scalar quantity.
• Displacement is the shortest distance between the initial position and the final position of the body.
• Distance is the length of the total path travelled by a body.
• Speed is the total distance travelled per unit time.
• Velocity is displacement per unit time.
• Speed is a scalar quantity whereas velocity is a vector quantity.