Let's go over some math.
We can calculate the kinetic energy of the car by using the formula KE = 1/2 x mv^2
Where m is the mass of the vehicle and v is the velocity.
SUVs weight around 2000kg / 2 tonnes. Or 4410 pounds.
Like you said, she was driving at 5mph. For this calculation, we're going to have to convert from burgers/football to m/s, so the speed is ~2.24 m/s
KE = 1/2 x 2000 x (2.24)^2
The kinetic energy of the SUV of love and empathy is around 5,018 joules.
For comparison, a 9mm bullet has 300 - 400 joules of kinetic energy.
Now, converting this energy to Newtons is a bit tricky, because it depends on several factors. But we can estimate that the force inflicted by a SUV traveling at 5mph is between 5000 and 8000 N.
How bad is this? The femur, the largest and sturdiest bone in the human body, takes about 4000 N of force to break. All the other bones are far less resilient.
Draw your own conclusions from that.
Your point that even at 5mph a large vehicle is a serious danger to someone in its path is correct. (Especially as moving at 5mph is entirely possibly an immediate precursor to moving at greater than 5mph). But in the interests of not giving easy wins to your opponents, your calculations are too simplistic and have some fairly easy holes someone could poke at. You are talking as if there is total energy transfer.
The cap on the amount of energy that can be transferred (simplifying) is the amount of energy required to accelerate the impacted body up to the same speed as impacting body. Or to illustrate: an oil tanker moving at 1mph would have orders of magnitude more energy again, but would likely not harm you because the most it would accelerate you up to would be 1mph and your body can handle that amount of energy transference.
Assume that the officer weighs 70kg. If the car impacting him is at 5mph or 2.24m/s then the most he is going to be moved backwards is 2.24m/s and if we presume he goes directly from 0m/s to 2.24m/s in say half a second then the acceleration is 2.24/0.5^2 (that is meters per second per second). That is an acceleration of 8.96m per second per second.
Plugging this into Force = mass x acceleration, gives us:
F = 70kg x 8.96 = 627.2N
As you can seem 627 newtons is a lot less than the 5,000 to 8,000 newtons you estimate. That would only apply if he were braced against a wall or something and couldn't displace.
Now the 0.5 seconds I estimated for the duration over which the acceleration takes place is just rough estimate. We could actually work out something more accurate by looking at how quickly a vehicle at 5mph moves through the space he occupies. But I don't think that's worth doing. The important thing is to understand the principle that the faster the vehicle is going to faster the rate of acceleration and thus the faster the rate at which energy is transferred. Would you rather be hit by an oil tanker going 1mph or a car going 60mph? We all instinctively know it's the former but the mathematical explanation of why is because the latter will accelerate you far more and it's the rate of energy transference that is the issue, not the total energies involved.
On the whole such exercises are fun but risk opening yourself up to counter arguments if too simplistic. You're right but having half of an answer means someone can just have an easy "win" of pointing out you're missing stuff. And other factors matter as much such as point of impact. If the same car and speed hits me right in the hip that's a lot worse than if I have my hands out ready and the bonnet / hood hits them. Same with your bullet example - way less energy but the far greater speed and the fact it is focused on a point means the energy isn't turned into displacement you might handle but goes right through your body.
Anyway, it's a tangent of course but as you laid out half of the journey I felt compelled to take it a bit further. The half version means someone can say "it's impossible for the car to transfer the 2000N you say, argument dismissed". It's fun to illustrate and useful to have in your back pocket if someone says "but the car was only going 5mph". But the key factor is really what it was reasonable for the officer to think at the time. And a car accelerating into you at 5mph is already capable of killing or crippling you if you were run over and you have no way of knowing that 5mph is not going to continue to accelerate further.
I believe she was just trying to leave. But she chose to do so through where someone was standing. He was justified in acting defensively, imo.
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