Question

A car traveling west in a straight line on a highway decreases its speed from 30 meters per second to 23 meters per second in 2 seconds. The car's average acceleration during this time interval is

Answer 1

Use the equation Vf=Vi+A(t)
Rearrange it so A is isolated: A= Vf-Vi/t
A=(23-30)/2
A=-3.5m/s^2

Answer 2

u1= 30m/s
u2= 23m/s
t=2s
a=(u2-u1)/t
a=-7/2=-3.5 m/s^2