8.15m. La altura de la casa de la cual se deja caer un objeto que tarda en caer
es de 8.15m.
La clave para resolver este problema es mediante caída libre, la velocidad inicial del objeto es 0 por lo que podemos calcular la altura h de la casa mediante la relación
.
Conocemos la gravedad
y el tiempo en que tarda en caer el objeto
, sustituyendo los valores tenemos que:

Here in the above situation when boy pushes the girl there will be equal and opposite force on boy as per Newton's III law.
Due to this action reaction law boy will also go back with some speed.
Since there is no external force on this girl + boy system so we can use momentum conservation principle here.
As per momentum conservation




So boy will go back with speed 0.2 m/s
Part b)
Since the boy and girl will always exert same force on each other by Newton's III law so it has no it matter whether the boy pushed the girl, the girl pushed the boy, or they put their hands together and pushed each other away.
As in all above cases the as per Newton's III law the force on them is always equal and opposite.