You push a heavy crate. at first it doesn't move. you push harder, and it finally starts to move, but you still have to exert some force to keep it moving at a constant velocity. explain.

Because, if something is 40N and you push it with 10N, you aren't following the laws of physics. You must exert an equal or greater force on the object. You have to keep this up because you must keep it the same amount if it is going at a constant.

They are asking me the same question

Nps pollution is caused by rainfall or snowmelt moving over and through the ground. nonpoint source pollution can include: excess fertilizers, herbicides and insecticides from agricultural lands and residential areas. oil, grease and toxic chemicals from urban runoff and energy production