When the sum of all the forces acting on a block.

D. engine-coolant temperature is the answer : ) =)

. we do not care the other details; the average velocity is only concerned with the  displacement rather than the  distance traveled. displacement is the change in position, or the "straight-line vector from the initial position to final position".

For the bullet,  the net force on the bullet: an fbd would look like a dot with a horizontal "friction" force protruding from one end.by newton's 2nd law: we can solve for acceleration since we know  and .we know that  (final velocity is bullet not moving), . we can use the following kinematic equation to get  , or the displacement.so it penetrates  m.