Vertical Motion 4

The slope of the v-t graph gives the acceleration of the fish when it is in air. When in air, the only force acting on the fish is gravity, always with a downward acceleration of g (i.e. 9.81 m/s^2). Hence,

(1) The acceleration (slope of v-t graph) remains the same irrespective the fish is going up or falling down.

(2) Acceleration due to gravity is independent of the mass of an object. That, the slope of the v-t graph is independent of the fish mass.