4. Find the average acceleration of a northbound subway train that slows down from 12 m/s

to 9.5 m/s in 0.8 s.

-3.125m/s^2

Step-by-step explanation:

Average acceleration = v-u / t

That is initial final velocity v minus initial velocity u divided by the time t In seconds.

From the question,

v = 9.5m/s

u = 12m/s

t = 0.8 secs

Using the above formula,

We have

average a = 9.5 - 12 / 0.8

= - 2.5/0.8

= - 3.125m/s^2

Negative answer indicates that the train was decelerating