PHYS 1301W Lecture 1: Waves and Frequency

A 6.4 g bullet leaves the muzzle of a rifle with
a speed of 335 m/s.
What total constant force is exerted on the
bullet while it is traveling down the 0.87 m
long barrel of the rifle?
Answer in units of N.

I need an explanation of how to do the following type ofproblem.
"A five gallon pail is filled to the top with a oven dry sand witha specific gravity of 2.55. There are no voids in the total volume.How much does the sand in the pail weigh?"