A 42-kg girl walks to the top of stairs that are 3.0-m high. How much gravitational potential energy does the girl gain?

Can somebody explain to me how newton's 3rd law relates to momentum? ~ap physics 1

Although longitudinal waves can travel through all media types what is the disadvantage of this type of wave transmission? a) he efficiency of he wave transmission is greatly diminished as the media becomes less dense b) the oscillation of one set of particles has a huge impact on neighboring particles c) particles become too close together as they bump into each other making it more likely to hit other particles down the line

How is zig zagging a form of acceleration?