✔ 最佳答案
You are right in the sense that the forces is in action and reaction pair, so the magnitude is the same. However, mass of the truck and the private car (with drivers) are totally different. So by a= F/m, acceleration of two drivers are different in magnitude, hence the resultant velocity of two drivers are different.
As a result, as private car is lighter, its acceleration is larger and the change of momentum is also larger.
[Change of momentum = m(v-u) ]
E.g. v=u=10 in magnitude, where v and u are in opposite directions, change of momentum = m(10-(-10)) = 20m, so when the resultant velocity is larger due to smaller mass, change of momentum is greater.
