A rider on horse back falls when horse starts running all of a sudden because

A mass of $1 kg$ is suspended by a string $A$. Another string $C$ is connected to its lower end (see figure). If a sudden jerk is given to $C$, then

An astronaut accidentally gets separated out of his small spaceship accelerating in inter stellar space at a constant rate of $100 \;m/s^2$. What is the acceleration of the astronaut the instant after he is outside the spaceship ? (Assume that there are no nearby stars to exert gravitational force on him.)

A bird is sitting in a large closed cage which is placed on a spring balance. It records a weight of $25\,N$. The bird (mass $m = 0.5 \,kg$) flies upward in the cage with an acceleration of $2\,m/{s^2}$. The spring balance will now record a weight of …….. $N$

Inertia is that property of a body by virtue of which the body is