Question

A train moving at a speed 72 km/hr is brought to rest in 40 seconds.
Find the retardation and the distance covered.
[Hint: 72 km/hr 72000/3600 m/s = 20 ms-1]​

Answer 1

Answer:

distance is 800m

Explanation:

speed * time

20* 40

=800

Answer 2

Answer:

Retardation (Negative accelaration) = 0.5 ms^-2, Distance covered = 400 m.

Explanation:

To find retardation (Negative accelaration):-

Given:-

v = 0

u = 20 ms^-1

t = 40 s

a = ?

We know,

v = u + at

Therefore,

a = (v-u)/t

Substituting values,

a = (0-20)/40

  = -0.5 ms^-2

Therefore, the retardation would be 0.5 ms^-2

Now, to find the Distance covered,

We know,

v^2 = u^2 + 2as

Therefore,

s = (v^2 - u^2)/2a

Substituting the values,

s = (0^2 - 20^2)/2*-0.5

  = -400/-1

  = 400m.

Q.E.D

Hope this helps, have a great day!