I have two Inertia-acceleration questions,

1. if mass were to be decreased (which decreases inertia), what would happen if the object with decreased mass were thrown and it hit something (a wall, for example)?

2. If the mass (inertia) of a person were to decrease, what would happen to the person's running, jumping, lifting, etc.

Please answer, or at least don't laugh, I'm new here.

1. If you decrease the mass you will decrease the impact.

2. If the inertia is decreased than it will take less energy for the person to stop/jump/lift. (considering the running speed and jumping height are the same.)

Do the experiment!

Get two objects, one light, one heavy. Try throwing them against a wall.
Get two people, one light, one heavy. Get them to jump, run, lift, etc.