What Is the Velocity After Two Cars Collide?

[BvU]

Boy, if I have ever seen a plea for metrication, this is the one !

On the other hand it's good to realize -- as entro did -- that momentum really has the dimension mass times length divided by time, in whatever units are in fashion !

 

[mfb]

You are welcome.

Oh, the SI system does not get off quite so easy either.

If you weigh yourself on the bathroom scales and get 68 kg (150 lbs).

This is also Force units. So $kg_f$

And the $G_c$ for the SI system is $9.8 kg*m/kg_f/s^2$

So $kg_f = kg_m$

If you step on the same scale on the moon, you would only weigh 11.6 kg_f. But when you do the conversion, you will still be 68 kg mass.From that other source.

No, the SI doesn't have that mess. There is no such thing as "kg_f".
The bathroom scale measures a force of 667 N and converts it for you to m=F/g = 68 kg.
On the Moon the bathroom scale measures ~110 N and converts it (wrongly) to about 11 kg because it is not calibrated for use on Moon. A properly calibrated scale there would convert 110 N to 68 kg as well. If scales would be used in different environments frequently, one would add a test mass to the scale to make it self-calibrating.