力學問題求解

1 and 2 are right

作用力的功和反作用力的功一定一正一負

By Newton's thrid law, action force(作用力) and reaction force(反作用力) are always in the opposite directions, which means that if we define one direction is positive, then the opposite direction is obviously negative


作用力的大小和反作用力的大小一定相等

Also, by Newton's third law, the magnitudes of both the action force and the reation force are always the same. A good example is that when you try to hurt someone with your hand it is as if you are hurting your own hand