How does inertia affect a person who is not wearing a seatbelt during a collision?

They are sent forward with force with a potential fatal consequence. 

They are sent forward, because of momentum (Inertia). 

Lnertia is the resistance of any object to a change in its state of motion. This means it is the tendency for an object to stay moving at a constant rate in a straight line. So if a car stops suddenly, as what happens in a collision, the unbelted passenger would continue at the same rate of speed forward until they met resistance in the form of the windshield or dashboard. Ouch!

Wear your seatbelt!!

This ain't even a question. speak english