A question about speed & Acceleration?

Question

A truck covers 45.0 m in 8.00 s while smoothly slowing down to final speed +2.00 m/s.
a. Find its original speed in m/s
b. Find its acceleration in m/s2

Answer 1

a)

s=(v-u/2)t

s=45
v=+2
t=8

s =(v-u/2)t
45 =(2-u/2)8
u = -9.25m/s

b)

a=(v-u)/t

v=2
u=-9.25
t=8

a=(v-u)/t
=2-(-9.25)/8
=1.40625
=1.41m/s2 (to 3 sig fig)

Answer 2

v1=2 m/s; s=45 m; t=8 s; find v0, a
a. v(average) = s/t = 5.625 ; v0 = 2v(average) - v1 = 9.25 m/s
b. a = (v1 - v0)/t = -.90625 m/s^2