Friction? For example, like when a car's tires skid on rough concrete.
B, a disurbance would make it unstable and affect the center of mass, which would then affect the equilibrium.
Answer:1.5
Explanation:
Given
mass of first cart 
initial Velocity 
mass of second cart 

In the absence of External Force we can conserve momentum




Final kinetic Energy of two masses



Initial Kinetic Energy




Answer:
Frequency describes the number of waves that pass a fixed place in a given amount of time.