1.

the collision shown here is

elastic

inelastic

2.

any work being done is done against the force of

friction

mass

3.

with an inelastic collision, you have to use the conservation of

matter

momentum

2. Friction

3. Momentum

Explanation:

For elastic collision, the total kinetic energy before and after collision are same while for inelastic collision, kinetic energy is converted to other forms apart from kinetic energy for example we get sound energy or rotational energy. Since in this case there's no diagram, we can't make a conclusion. However, in real life, all collisions are inelastic

2

Work is always done against frictional force

3

The law of conservation of momentum is used in an inelastic collision

we need to know the time interval during which the force acts. impulse of force = momentum change