# Car accelerating behind me up to 40mph

1. Dec 9, 2004

### jimmy p

Ok these are a couple of strange questions.

If you were travelling at a constant speed eg, 30mph and you hit someone, would it do more damage to them than if you were accelerating towards them up to 30mph when you hit them?

And this one, I know what the answer should be but I cant get my head round it. If I were driving at a constanst speed, say 40mph, and there was a car accelerating behind me up to 40mph, if I looked in my rearview mirror, would they be coming towards me, retreating from me, or staying in the same place? I think it is retreating from me...

Thanks

James

2. Dec 9, 2004

### ceptimus

If you assume that in the impact the driving force on the wheels stops immediately on contact, or is negligible compared to the impact force, then it shouldn't make any difference whether the car is going at a constant speed or accelerating or slowing down.

On the second question, you are right. As long as it is going slower than you, it will recede. When it reaches your speed, it will stop receding and maintain a constant distance. In order to advance on you, it has to be going faster than you are.

3. Dec 9, 2004

### jimmy p

So I still know something about physics! Thanks!

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