Agolf club exerts an average horizontal force of 1000 n on a 0.045 -kg golf ball that is initially at rest on the tee. the club is in contact with the ball for 1.8 ms. what is the speed of the golf ball just as it leaves the tee?

The impulse (the variation of momentum of the ball) is related to the force applied by

where  is the variation of momentum, F is the intensity of the force and  is the time of application of the force. 
Using F=1000 N and , we can find the variation of momentum:


This  can be rewritten as

where  and  are the final and initial momentum. But the ball is initially at rest, so the initial momentum is zero, and

from which we find the final velocity of the ball:

The duration of a photographic flash is related to an rc time constantly

Independent variable is something that is changed in a experiment.