Answer to Question #16762 in Mechanics | Relativity for leslie
If a man pushes on a crate with 10 newtons of force and Fred the goat pushes with him with another 10 newtons of force, what is the net force of Fred and the man on the crate?
The answer sufficiently depends on the direction that Fred is pushing the crate in. If it coincides the direction of a man, then the forces add:
F = 10[N] + 10[N] = 20[N].
Otherwise, if their directions are opposite, then the forces subtract:
F = 10[N] - 10[N] = 0[N].