A 30-kg girl on friction-free roller blades pushes away a 25-kg boy also on roller blades at 1 m/s. The girl’s speed is

When an apple falls to the ground, momentum is transferred to the ground. The momentum absorbed by the ground is

An iron ball and a wooden ball of the same size are dropped from a tall tower. Taking air resistance into consideration, the object to hit the ground first will be the

The amount of gravitational force that acts on a space vehicle that orbits Earth is

A 5-kg fish swimming at 1 m/s swallows an absent-minded 1-kg fish swimming toward it at 4 m/s. The speed of the larger fish after lunch is

If a monkey floating in outer space throws his hat away, the hat and the monkey will both move

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

A popular swinging-balls apparatus (Newton’s cradle) consists of a series of identical elastic balls suspended by strings so they barely touch each other. When two balls are pulled away from one end and released, they strike the row of balls and two balls pop out from the other end. If instead, one ball popped out with twice the speed, this would violate the conservation of

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