Question

If the force exerted by a fish on the tip of a fishing rod is 4.0 N, what force (including direction) must
the fisherman exert. The rod is being held at angle of 300 above the horizontal. Ignore the rod’s
mass, and assume the rod is pivoted in the fisherman’s other hand.

Answer 1

Draw a FBD of the rod wrt the ground. The forces consist of
(1) Due to the fisherman
(2) Due to the fish (in the question, and in your diagram)
Now, at that instant, the net ext. force on the rod must be zero, as it's mass is neglected.
Thus the force on the rod due to the fisherman is equal (also equal to 4 N) and opposite in direction to that applied by the fish on the rod.