During inelastic collision between two bodies, which of the following quantities always remain conserved?

Two inclined frictionless tracks, one gradual and the other steep meet at A from where two stones are allowed to slide down from rest, one on each track as shown in figure. Which of the following statement is correct?

The potential energy function for a particle executing linear SHM is given by $$V(x)=\frac{1}{2} k x^2$$ where $$k$$ is the force constant of the oscillator (Fig). For $$k=0.5 \mathrm{~N} / \mathrm{m}$$, the graph of $$V(x)$$ versus $$x$$ is shown in the figure. A particle of total energy $$E$$ turns back when it reaches $$x= \pm x_m$$. If $$V$$ and $$K$$ indicate the PE and KE, respectively of the particle at $$x=+x_m$$, then which of the following is correct?

Two identical ball bearings in contact with each other and resting on a frictionless table are hit head-on by another ball bearing of the same mass moving initially with a speed $$v$$ as shown in figure.

A body of mass 0.5 kg travels in a straight line with velocity $$v=a x^{3 / 2}$$ where $$a=5 \mathrm{~m}^{-1 / 2} \mathrm{~s}^{-1}$$. The work done by the net force during its displacement from $$x=0$$ to $$x=2 \mathrm{~m}$$ is