Take into account that the formula for the momentum is:
p = m*v
where,
v: velocity
m: mass
1) In this case, you have:
mA = 35 kg
vA = 5 m/s
The momentum is:
p = (mA)(vA) = (35 kg)(5 m/s) = 175 kg*m/s
2) If son B pushes on son A with a force of F = 40N, then, by the Newton third law, son A pushes on son B with the same force F = 40 N
3) To determine the acceleration of son B, use the following formula:
F = mB*a
where a is the acceleration. If you solve for a and repalce the values of other parameters, you obtain:
a = F/mB
a = 40 N/ 20 kg = 2 m/s^2
