A stone is thrown vertically upward. At the top of its vertical path the force acting on it is

If there were no gravity, a ball thrown upward at an angle would follow a straight-line path. Due to gravity, however, at the end of 1 s it is

A push on a 1-kg brick accelerates the brick. Neglecting friction, to equally accelerate a 10-kg brick requires the force to be

With no air resistance, a projectile fired at 50° has the same range as if it were fired at

If a weighted air-filled balloon sinks in deep water, it will

An open freight car rolls friction-free along a horizontal track in vertically pouring rain. As water accumulates in the car, its speed

A flat piece of iron is tightly tied against top of a wooden block. The iron-wood block floats in a bucket of water. If the iron-wood block flips over so the iron is on the bottom, the water level at the side of the bucket

An astronaut floating alone in outer space throws a baseball. If the ball moves away at 20 m/s, the astronaut will move in the opposite direction at

Just after a big fish swallows a small fish, the momentum of the two-fish system is

The total momentum of a flock of identical birds could be zero only if the birds are