I wonder if bumpers of some cars automatically place the impact point (the bumper, if slamming into a solid object) below the center of mass. Most of the engine, and most of the car, is usually above the bumper level.
So the cause of the lift off is the forward pitch caused by the reducing grade of the hill, and the impact point being below the center of mass due to the lowering of the front of the car during braking. And also the forward pitch movement caused by the braking (front end going down, back end...
I think I have explained this many times and you have ignored me. The car's motion has a horizontal vector and a vertical vector. When the car hits the barrier, the front of the car is stopped in its horizontal and vertical motion. The rear of the car has nothing keeping it from going upward...
1st paragraph: If the car were a tiny particle, you would be right. The car is probably 9-10 feet long. While there is something preventing the front bumper from lifting up on impact, there is nothing preventing the rear of the car from lifting up on impact, hence the initiation of forward...
the instant when the front bumper is pinned on the obstacle during collision, is enough to initiate a forward roll rotation of the vehicle. Once that is started...an object that is in motion stays in motion unless a force changes that...it keeps going until a force stops it. That force is gravity.
First paragraph is not on the topic. I am not discussing a car flipping. It also makes no sense even if it were on the topic. There are plenty of other reasons for the car to have the rear wheels or all 4 wheels lift off, besides this very narrow set of criteria.
Second paragraph: part a...
I do think that without braking prior to impact, the impetus for the car to lift would be much less, and would require a higher overall velocity of the car. If the car is braking and the front end is already dipping and the rear is already rising, when impact happens, it takes very little...
Part of what I am trying to describe is the situation in which the front tires come just barely up off the road, also. In the braking on level ground models, the front of the car goes DOWN and the rear of the car goes UP. This does not look like a recipe, by itself, for both sets of wheels...
Yes, the impact point is low because the front of the car is already dipping down because of the front-loading effect of braking, as you can see in the more recent braking video I sent you. This is still a result of the car's own motion. The rear of the car also has an upward velocity vector...
Watch the video of the racing car crash compilation I put in the introduction. The upward moving car crashes into a straight wall that is taller than the car. This makes it clear that the barrier is not causing the upward lift. The car's momentum is causing the upward lift. We are talking...
Homework Statement
This is a video of the phenomenon. Start at 5:08 in this video and watch the next two crashes. That first one, where the car hits a wall, straight on, is the most helpful. The phenomenon is that when a car going uphill crashes, it has an upward speed/momentum vector...
Most of the answers to your question are in the stated problem and the mass cancels out. My calculation begins when brakes are applied, so driver reaction is not part of the calculation.