Question

两个共点力同向时合力为a，反向时合力为b，当两个力垂直时合力大小为（    ）

A.        B.          C.         D.

Answer 1

解析：假设两个力分别为F₁、F₂，则：

同向时：F₁+F₂=a                                                        ①

反向时：F₁-F₂=b                                                        ②

当两力垂直时：F=                                                                  ③

由①②得：F₁=(a+b)/2，F₂= (a-b)/2

代入③得：F=

答案：B