1548134356814125471196.jpg Sr how will I decide that there is no external impulse and friction is impulsive
both the statments are in correct.
in case 1 there is no external impulse on ball and mass system. case 2 friction is impusive as normal with the ground is impulsive
We know that f=μN(only during slipping motion, for no slipping frictional force is equal to applied force RESISTING friction). Since friction is proportional to normal reaction, it will be impulsive only when normal force is impulsive.
Thus, if in a situation there is a sudden change in normal force, friction will be impulsive