Answer:
The average force times the time of interaction equals the change in momentum
Step-by-step explanation:
The impulse-momentum theorem states that impulse (equal to the average force times the time of interaction) is equal to the change in momentum:

where
I is the impulse
F is the average force
is the time of the interaction
is the change in momentum
We can demonstrate this theorem, by re-writing the force as mass (m) times acceleration (a):

The acceleration is equal to the change in velocity divided by the time interval:

And by simplifying
, we get:

which is equal to the change in momentum.