Originally Posted by GreenFrog
In CG's scenario above, is that the same as getting rear ended while stationary by a car going 20 MPH?
Well, not the same as a car because of the huge mass delta with a freight truck, but from a physics standpoint it is the same linearly (assuming the stationary car is in drive and not park or neutral).
What Vader and brokencycle said about losing control / spinning is obviously different (explained a bit below - the impulse is the same, but the consequences are different from a loss of control standpoint)
Impulse would be the same in both cases however because the relative velocity delta and in turn the momentum delta are the same - i.e. the reference frame is the same.
Edit: To add additional clarification, the t1-t2 (the time the truck would be imparting a force on the car) would be the same because of the reference frames being the same. Should also add, at 60 mph, the car is being accelerated beyond 60 mph by some amount. At 0 mph, the car is being accelerated beyond 0 mph by roughly the same amount, so the dangers that come with that would be different as well.
Edit2: OCD me - there would some minor differences in accounting for static and kinetic coefficients of friction of the tires and any aerodynamic effects at speed - but those would be near trivial in this case.
tl;dr: Physics wise, it's roughly the same with the exception that you're being asked to control a car being plunked into at 60 mph vs. 0 mph and we all have reaction times.Edited by ramuman - 7/24/16 at 3:03pm