The right half will be a new bar magnet of 2cm with north pole on the right side and south pole on teh left.
Explanation:
Let the speeds of father and son are
. The kinetic energies of father and son are
. The mass of father and son are 
(a) According to given conditions, 
And 
Kinetic energy of father is given by :
.............(1)
Kinetic energy of son is given by :
...........(2)
From equation (1), (2) we get :
..............(3)
If the speed of father is speed up by 1.5 m/s, so the ratio of kinetic energies is given by :


Using equation (3) in above equation, we get :

(b) Put the value of
in equation (3) as :

Hence, this is the required solution.
Answer:
a=3.53 m/s^2
Explanation:
Vo=0 m/s (because he is not moving at the start)
V1=15 m/s
t= 4.25 s
a = (V1-Vo) / t = 15/4.25 = 3.53 m/s^2
Velocity is distance/time
so 150/7200=.0208km/s
unless you have to convert it to miles or something else. but use the formula!