I like playing ________ football. John likes playing ______ piano.
甲同学说:每人分别用力10N合力应该为20N,所以示数为20N.
乙同学说:两个力方向相反,应为平衡力,大小相抵消,所以示数为0.
丙同学说:弹簧侧力计的示数为一个人用的力,即为10N.