a force is something that causes change in motion . what provides the force that made the cart speed up

the unbalanced force

Explanation:

An unbalance forces are defined as the forces which causes a change in the speed or velocity of a moving object. A force causes a change in the motion of a body and an unbalanced force causes the body to change its velocity and speed or a change in its direction.

An unbalanced force will start movement in a static object or it can cause to speed up the moving object or it can cause to stop the moving object.

Thus an unbalanced force causes the cart to speed up.

the total distance that martina travels that day is

(distance from home to mom's office) plus (distance from mom's office to school)

plus (distance from school to library) plus (distance from library to friend's house)

plus (distance from friend's house to martina's house).

(we don't know what any of these distance actually is.)