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

The result of inertia due to not wearing a seatbelt will result in the passenger becoming some sort of a missile .
The weight of the passenger pluse the speed of travel prior to the collision will be multiplied together to equal the force their body will endure.
For ex. the force a person will be subjected to for a passenger weighing 100 pounds, in a vehicle traveling at 60 mph, will be the equivalent of 6000 pounds hitting a brick wall.
I hope this helps:)