# Newton's Second Law

1. Feb 17, 2007

### Annubes

I'm having a hard time understanding this.
If a car that has a constant acceleration hits me lets say at 10km/h then at 100km/h will it exert the same amount of force on me? F= ma mass and acceleration are constant. But this doesn't seem right, does it?

Do you guys know any good website or a book that has questions that will test my conceptual understanding of newton's laws.
Thanks:tongue2:

2. Feb 17, 2007

### e(ho0n3

If you're talking about hitting, you have to consider momentum, which does take into account the velocity of the car.

3. Feb 17, 2007

### JeffKoch

The force accelerating the car is not the same as the force you'd experience when it hit you. F=ma works for the car, but the force you feel is the change in your momentum delta-P, divided by the time it takes to change momentum, delta-t.

Consider the case of a car that isn't accelerating at all, just moving at constant speed. When it hits you, there's no accelerating force F=ma, but you'll still feel a force on impact.

4. Feb 17, 2007

### Annubes

ahh... ok. I guess I have to wait till we get to momentum to fully understand this. thanks