A helicopter is hovering motionless above a disabled boat, while rescue workers use a rope to lift an injured sailor. While that sailor is being lifted upward, the net force on the motionless helicopter is(A) downward and equal to the sailor's weight. (B) zero. (C) upward and equal to the sailor's weight. (D) downward and equal to the sailor's weight plus the helicopter's weight.

The keyword for the solution of this problem is the word “motionless”. We are told here that the helicopter is motionless, this means (according to Newton’s 1st law of motion) the net force on the helicopter is zero.

Now, if we want to go further in the analysis, we can draw a Free Body Diagram (FBD) of this situation (figure attached), assuming there are no forces in the x-axis.

Nevertheless, in the y-axis we have the weight [tex]W[/tex] which is equal to the weight of the helicopter [tex]W_{H}[/tex] plus the weight of the sailor [tex]W_{S}[/tex] (assuming the rope is weightless):

[tex]W= W_{H}+ W_{S}[/tex]

And the lift force [tex]L[/tex] which is with the same magnitude but in the opposite direction of the weight:

[tex]L=W[/tex]

Therefore, the correct option is B.