when a gun is fired a very large force acts on the bullet for a very short time. formula that's given: force x time = change in momentum (kg m/s) an average force of 4000 acts for 0.01 seconds on a bullet of 50g mass. DONE THIS PART b. the bullet is fired horizontally. in the short time that it takes for it to reach it's target, its horizontally has fallen by 80% of its initial speed. explain why the speed of the bullet has decreased so quickly. c. calculate the percentage of its original Kinetic energy the bullet still has when it reaches its target.