When is the structure and composition of a community expected to remain unchanged?

What is meant by species composition of a community?

A body is moving along the boundary of a square plot of land with constant speed. Does its velocity remain unchanged ?

Assertion : A parallel plate capacitor is connected across battery through a key. A dielectric slab dielectric constant K is introduced between the plates. The energy which is stored becomes K times. Reason : The surface density of charge on the plate remains constant or unchanged.

Is it possible that productivity and diversity of natural community remain constant over a time period of, say one hundred years?

In an LCR-circuit, capacitance is changed from C to 2 C. For the resonant frequency to remain unchanged, the inductance should be changed form L to

Prove that if no external force is acting on a body. Its momentum will remain unchanged.

A constant force acting on a body of mass 3.0 kg changes its speed from 2.0 m s^-1 to 3.5 m s^-1 in 25 s. The direction of the motion of the body remains unchanged. What is the magnitude and direction of the force ?