Question

question 19 1 pts action and reaction pairs of forces are independent of time. always act simultaneously. may or may not act simultaneously. question 20 1 pts the force that propels a cannonball when fired from a cannon is in some cases, equal and opposite to the force the ball exerts on the cannon. huge compared to the recoil force on the cannon. equal and opposite to the force the ball exerts on the cannon.

Explanation:

For Question 19, Newton's third - law states that action and reaction forces always act simultaneously. For Question 20, according to Newton's third - law, the force that propels the cannonball and the force the ball exerts on the cannon are an action - reaction pair, so they are equal and opposite.

Answer:

Question 19: always act simultaneously.
Question 20: equal and opposite to the force the ball exerts on the cannon.