Question

a moving train is brought to rest within 20 seconds by applying brakes find the initial velocity if the retardation due to application of brakes is 2 M per second square

Answer 1

v = 0 m/s
t = 20 s
a = - 2 m/s^2
Using 1st Equation of Motion,
v = u + a•t
=> u = v - a•t
=> u = 0 m/s - ( - 2 m/s^2)•(20 s)
=> u = 40 m/s .

Answer 2

Given:

• Retardation is 2 m/s².
• Time taken to stop is 20 sec.

To find:

• Initial velocity of train ?

Calculation:

• Since the train stops, the final velocity (v) will be zero.

Applying EQUATIONS OF KINEMATICS:

$\sf \therefore \: v = u + at$

• Value of 'a' will be -2 m/s², as it is negative acceleration (i.e. retardation).

$\sf \implies \: 0 = u + ( - 2)(20)$

$\sf \implies \: 0 = u - 40$

$\sf \implies \: u = 40 \: m/s$

So, initial velocity of train is 40 m/s.