Why can it be said that there is no such thing as an isolated force in nature?

$A$ spherical body of mass $100 \,g$ is dropped from a height of $10 \,m$ from the ground. After hitting the ground, the body rebounds to a height of $5 \,m$. The impulse of force imparted by the ground to the body is given by: (given $g = 9.8 \,m/s^2$)

$A$ force of $50\, dynes$ acts on a body of mass $5\, g$ which is at rest for an interval of $3\, seconds$. The impulse is:

$A$ ball of mass $60 \ g$ hits a wall with a velocity of $4 \ m/s$ and rebounds with the same velocity. The change in momentum in $kg \cdot m/s$ is:

What is impulse of force? Write its unit and dimension.

The $F-t$ graph for an object is shown in the figure. What will be the magnitude of the change in momentum $(\Delta p)$ in the interval of $0.03\, s$ from the start?