In a collision an object experiences impulses , this impulse can be determined by

In a collision an object experiences impulses, this impulse can be determined by the product of net force exerted upon it in the specific course of time.

Explanation:

An object experiences impulse due to the force exerted upon it in a particular time period.

i.e.

Where,

F - Force acted upon the object

- time interval for which the force act

According to the definition of Impulse, it is the integral of force (F) that acts upon any object over a time interval ∆t. It produces an equivalent change in the momentum and that too in the same direction as of the applied force (F).

Therefore, in order to find the impulse on an object, we have to find the force acted on it in a specific time interval.

the pull of gravity on the rocket decreases