text: how can we calculate the force of the collision & the duration of the collision?   the formulas it seems your looking for are:  p=mv=j=ft  where p, v, and t actually have a the symbol delta in front of them meaning "change in"  p is momentum which equals mass times the change in velocity and j is impulse which equals force x time.  because the change in momentum is equal to the impulse, you can usually set mv=ft.  you should be given the mass and velocity, and either force or the change in time(duration) in order to solve for the other one.  if the question is asking for both, then you probably have to find force first in some other way, then use that formula.  if you need to find the force in some other way, just think about all of newton's laws and stuff that you've learned and use them with the rest of the information that the problem gives you, and you should be able to come up with something... if not, post the whole question here and ill try to help :)