Question

1. why is kinetic energy not conserved in a partially elastic collision?

partially elastic collisions occur in a closed system, which allows for energy and mass to be added or lost.
one of the objects experiences deformation.
the final velocities of the objects change.
momentum is not conserved in a partially elastic collision, which affects the kinetic energy.

Explanation:

In partially elastic collisions, some kinetic energy is converted into other forms (like potential energy from permanent deformation of objects, heat, or sound). The other options are incorrect: partially elastic collisions occur in closed systems where mass/energy isn't added/lost; velocity changes happen in all collisions but don't explain kinetic energy loss; momentum is conserved in all closed-system collisions, including partially elastic ones.

Answer:

One of the objects experiences deformation.