If you hit a car, your speed is probably between 5 and 25 mph.
If the car hits you, it's speed is probably between 5 and 80 mph.
(And whichever vehicle is moving faster is the one that's most likely to be deemed to have hit the other one. The only likely exception to that is probably when hit at close to a 90 degree angle.)
Lower speeds tend to result in injuries, but anything over 40 mph is quite likely to result in death.
Also, if the car hits you, there's the chance of it running *over* you, but if you hit it it probably won't, especially if it wasn't moving at all.