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

or