Question

两个力F1=(1,1) F2=（4,-5）作用于同一个质点 使该质点从A（20,15）移到点B（7,0）

Answer 1

B - A =（7,0）-（20,15) = (-13,-15)

1）.F1,F2分别对质点所做的功

A1 = (1,1)· (-13,-15) = -13 - 15 = - 28

A1 = (4,-5)· (-13,-15) = -52 + 75 = 23

2）.F1,F2的合力F对质点所做的功

F1 + F2 = (1,1) +（4,-5）= (5,-4)

A = (5,-4)· (-13,-15) = -65 + 60 = -5