To everyone who said put the front wheels onto a scale and that will tell you how much force is required to lift the front end… you are wrong.
To everyone who said the car itself is acting as a lever, so you need to consider the distance from the car’s center of mass to the fulcrum (the rear axle in this case) and the distance from the fulcrum to the point where you’re lifting (the front bumper in this case)… you are right.
To illustrate why the second answer is right and the first answer is wrong, imagine a car which has a very very short wheelbase, so short that the front wheels and the rear wheels are almost touching each other. How easy would it be to push down on the front bumper, causing the rear bumper to lift off the ground an equal amount? How easy would it be to lift up the front bumper, causing the rear to go down? Very easy indeed, even if the car is very heavy. It’s all about leverage.
If you have a 1500 kg car with a 2.8 meter wheelbase and 4.8 meters overall length, and we assume that the center of mass is exactly in the middle and the front bumper and the rear bumper are the same distance from the middle, then…
- The front bumper is 3.8 meters from the rear axle.
- The center of gravity is only 1.4 meters from the rear axle.
- Lifting the front bumper 1 meter only lifts the center of gravity 37 cm.
- Lifting the front bumper 1 meter also causes the rear bumper to go down by 26 cm.
So you actually have a lever with a mechanical advantage of about 2.7, hence lifting 1500 kg 37 cm with this lever is just as easy as dead lifting about 550 kg a distance of 1 meter. The force required is about 5400 Newtons, or about 1200 pounds.
But if you tried to lift the exact same car at the front wheels instead of the front bumper, your lever would only have a mechanical advantage of 2.0 hence it would be like lifting 750 kg which would require 7350 Newtons (about 1700 pounds). That’s what you’d be measuring if you drove the front wheels of the car onto a scale, and it’s not the same as lifting it by the bumper (which is what Arnold did in the movie).