A firecracker before been lit has potential energy in it. It is chemical potential energy which is due to the explosives in it.When it is lit, it gets converted into heat,light and kinetic energy.
Newton's first law is sometimes known as the law of inertia. It is the law that states that an object at rest will stay at rest and an object in motion will stay in motion unless a force acts upon it. For example, if I was working with a wrench in space an it slipped, it would keep on going in one direction with a constant speed unless it hits something. Hope this helps!
Answer:
A and B are correct both are correct
Answer:

Explanation:
= Velocity of one lump = 
= Velocity of the other lump = 
m = Mass of each lump = 
The collision is perfectly inelastic as the lumps stick to each other so we have the relation

The velocity of the stuck-together lump just after the collision is
.