Question

a vehicle changes its velocity from 90 km/h to a dead stop in 10s. show that its acceleration in doing so is -2.5m/s^2

Answer 1

90000m/3600s = 25 m/s

a=0-25/10 ⇒ a = - 5/2 m/s^2

Answer 2

The Proof is as follows -

We have a vehicle changes its velocity from 90 km/h to a dead stop in 10s.

We have to show that its acceleration in doing so is -2.5m/$s^{2}$.

State the first equation of motion in one - dimension.

The first equation of motion helps us to calculate the final velocity of the body as follows -

v = u + at

According to the question -

initial velocity (u) = 90 km/h = 90000m/3600s = 25 m/s

final velocity (v) = 0 m/s        (since the body stopped)

time (t) = 10 seconds

Using the first equation of motion -

v = u + at

v - u = 10a

a =  $\frac{v-u}{10}$

a = $\frac{-25}{10}$ = - 2.5 m/$s^{2}$

The acceleration of the body will be :  - 2.5 m/$s^{2}$.

Hence Proved

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