deceleration or rėtardation i’m pretty sure (it won’t let me say the second word but it’s correct)
Mechanical waves travel the fastest in
solids and liquids because the
molecules are more closely packed together than gases, so energy is transferred
from one particle to another particle faster<span>.</span>
a) For the motion of car with uniform velocity we have ,
, where s is the displacement, u is the initial velocity, t is the time taken a is the acceleration.
In this case s = 520 m, t = 223 seconds, a =0 
Substituting

The constant velocity of car a = 2.33 m/s
b) We have 
s = 520 m, t = 223 seconds, u =0 m/s
Substituting

Now we have v = u+at, where v is the final velocity
Substituting
v = 0+0.0209*223 = 4.66 m/s
So final velocity of car b = 4.66 m/s
c) Acceleration = 0.0209 
Mass is measured in kg
Velocity is measured in ms^-1
Hope this is what you were looking for