Question

a cart initially moves to the right at constant velocity on a horizontal track. another cart is initially at rest on the same horizontal track to the right of the moving cart. when they collide, each cart exerts a force on the other. select all of the following statements that are true regarding these two forces. check all that apply
they always have the same magnitude.
they only have the same magnitude when the masses of the two carts are equal.
they are always in the same direction.
they are always in opposite directions.

Explanation:

By Newton's Third Law, the forces two objects exert on each other (action - reaction forces) always have the same magnitude and are in opposite directions, regardless of the masses of the objects. So "They always have the same magnitude" and "They are always in opposite directions" are correct. "They only have the same magnitude when the masses of the two carts are equal" is wrong because the magnitude of action - reaction forces doesn't depend on mass. "They are always in the same direction" is wrong as action - reaction forces are opposite.

Answer:

• They always have the same magnitude.
• They are always in opposite directions.