While the cart is moving along an aisle, it comes in contact with a smear of margarine that had recently been dropped on the floor. suddenly the friction force is reduced for -40.0 newtons to -20.0 newtons. what is the net force on the cart if the "pushing force" remains at 40.0 newtons? does the grocery cart move at constant velocity over the spilled maragine?

No, the velocity of the grocery cart will not remain constant, but instead will increase continuously

Explanation:

No the grocery cart will not move at constant velocity over the spilled maragine because as the frictional force is changed to - 20 N, the net force will not be equal to zero

Net force on the cart when frictional force is changed to - 20 N is 40 - 20 N = 20 N

As the force is positive, it means that the force is acting in the direction of motion of the cart and will increase the velocity of the cart as the force is acting in the direction of motion

∴ The velocity of the cart will not remain constant instead it will increase

their crystal patterns have been disrupted by stress