Since the protons are positively charged particles, they will repal each other. To bring them nearer, work has to be done against the force of repulsion and this will be stored up in the system as potential energy. So the potential energy of the system will increase.

The gravitational force on the comet due to the sun is not normal to the comet's velocity in general. Yet the work done by the gravitational force over every complete orbit of the comet is zero. Why? The gravitational force is conservative force.

The meteorite moves under the force of gravity therefore , its momentum goes on changing . But total momentum of meteorite and earth is always conserved

The energy of the bus has to go somewhere, and the momentum too, as they are independently conserved.

There is no external force as car is having constant speed

The energy is dissipated in the form of heat. The heat energy so produced is not available for work.

Work done is equal to Force (acting in the direction of displacement) times the displacement i.e. W=F.S where (.) is dot product.For the work done we need component of force along the direction of displacement but displacement and force are 90, at each and every point on the circular track and therefore the component of force along the direction of displacement will always be zero in case of a body moving in a circular track or a body performing circular motion. We know W=F.S or F.Scos(θ),...