Understand Momentum & Energy Conservation in Ballistic Pendulum Problems

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In a ballistic pendulum problem, momentum is conserved during the collision between the bullet and the block because there are no external forces acting on the system. However, energy is not conserved during this collision due to the presence of friction, which dissipates energy. After the bullet lodges into the block, the system moves upward, and energy conservation applies as gravitational potential energy is converted from kinetic energy. The confusion arises from the distinction between the collision phase and the subsequent motion of the block. Understanding these principles clarifies the conservation laws in different stages of the ballistic pendulum problem.
IKonquer
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In solving a ballistic pendulum problem, you can break it up into two parts:

(1) A bullet is fired and it lodges into a block.
Momentum is conserved because there is no net external force.
Energy is not conserved because there is friction between the block and bullet.

(2) Once the bullet is lodged into the block, the block moves up a certain vertical distance.

Could someone explain:

Why is momentum not conserved in this case?

Why is energy conserved in this case?
 
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Don't you have the parts in bold the wrong way around?
 

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