Question

Find the initial velocity of a train which is stopped in 20 seconds by applying brake the retardation due to break is 1.5 m per second square...

Answer 1

Final velocity (v)= 0m (as it comes to rest)
Acceleration (a)= -1.5m/s^2
Time (t)=20s
Let initial velocity be u
Using acceleration formula
a=(v-u)/t
-1.5 = (0-u)/20
-30 = -u
u=30
So, the initial velocity was 30m/s.

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Answer 2

Given:

• The final velocity = 0 m/s
• Time = 20 secs
• retardation = - 1.5 m/$s^2$

To Find:

• The initial velocity of a train.

Solution:

Using the first equation of motion,

v = u+at → {equation 1}

Where "v" is the final velocity, "u" is the initial velocity, "a" is the retardation or negative acceleration, and "t" is the time.

On substituting the values in equation 1 we get,

⇒ 0 = u + (-1.5)×20 {opening the bracket by bring out the negative sign}

⇒ 0 = u - 1.5 × 20 {multiplying the terms}

⇒ 0 = u - 30 {shifting the terms on LHS}

⇒ u = 30 m/s

∴ The initial velocity of a train = 30 m/s