A rock is rising straight upward in free-fall. What is Newton's Third Law companion force to the weight of the rock? A) the normal force from the ground on the rock
B) the throwing force from the person on the rock
C) there is no companion force because the rock is in free fall
D) the force of gravity from the rock on the Earth

D) the force of gravity from the rock on the Earth

Explanation:

When a rock  is under free fall , it is acted upon gravitational force by the earth . This is action force by the earth on the rock  . According to newton's third law , there will be a reaction force also .  Force is creating due to mutual attraction between earth and rock so rock will also exert gravitational force on the earth . Hence, that force will be reaction force .

Force due to rock on the earth will be reaction force , according to newton's third law.

truck y has a greater velocity than truck x.