Question

A moving train is brought to rest within 20 s by applying brakes. Find initial velocity if the retardation due to brakes is 1.5 m/s2

Answer 1

Answer :

Given -

• t = 20 s
• v = 0 m/s
• a = -1.5 m/s²

To Find -

• u = ?

Solution -

We know that, v = u + at.

Using it to find u,

⇒ 0 = u + (-1.5)(20)

⇒ -u = -30

⇒ u = 30 m/s

Hence, Initial Velocity = 30 m/s.

Additional Information -

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

Answer 2

Given,

• Final velocity = 0
• t=20s
• Acceleration =- 1.5m/s^2

To Find:-

Initial velocity

Formula used:-

V=u+at

Calculations:-

V=u+at

Now substituting the given values,

⇒ 0 = u + (-1.5)(20)

⇒ -u = -30

⇒ u = 30 m/s

Hence, Initial Velocity = 30 m/s.