Spider-Man
Professor Kakalios of the University of Minnesota said that Spiderman’s webbing could easily support his weight as he swings around Manhattan. Spider silk is one of the strongest materials in nature having a tensile strength of more than 5 times that of steel wire. (Tensile Strength is the ability of a solid substance to withstand tension.) Kaklios estimates that a strand of spider silk with a diameter of .6 cm could support his weight.
Cyclops
The X-Men’s Cyclops Shoots “force beams” from his eyes. Because Newton’s third law requires that for every force there is an equal & opposite reaction force, there is a force exerted on Cyclops, located in the area of his eyes, that is equal to the force resulting from the beam. The force from these beams would put such strain on his next that he would need enormous neck muscles to withstand the kickback, says Kaklios.
Dr. Henry Pym
Dr. Henry Pym created a serum that shrank him to the size of an ant & beam Ant Man. Later, he found another serum that turned him into Giant Man (later called Goliath), an 18m superhero with enormous strength. However, bigger doesn’t always mean stronger, according to Kaklios. The bigger an organism gets the more stress that it puts on it’s bones. Every time a doubles in size its area is increased by four times and its volume by eight. Volume is directly proportional to weight, while the area determines the strength of bone. So while Dr. Pym’s bones would have increased in strength 4 times for every time his size doubled, his weight would have increased 8 times. Eventually this would have caused his weight to overwhelm his bone strength, and he would risk breaking bones with every step.
Superman
Superman was a being born on the planet Krypton, a planet with ten times the gravity of Earth. When Superman came to Earth the affect would be similar to one of going to the moon, according to Kakalios. This explains Superman’s superior strength and his ability to leap tall building in a single bound. However, a planet that would have 10 times the gravity of earth would be difficult to come by, since the only planets massive enough to have this kind of gravity are generally gas giants. The only way that Kaklios kind explain this gravity in a rocky planet, is that the planet has a small amount of extremely dense material, such as a piece of a neutron star at its center. Of course a planet having a piece of a neutron star at its center would be extremely unstable, explaining the explosion of the planet Krypton.
The Flash
The Flash from DC comics has the ability to mover extremely fast. In one comic he ran around that planet in 80 seconds. Since energy has to be conserved, i.e., the work input is equal to the work output, the Flash has to eat enough to provide himself with energy to run that quickly. Kristin Barbieri calculated that there was no way that the Flash could possibly eat enough to power his bursts of speed.
Hawkgirl
According to Kakalios winged superheroes would need ridiculously large chest muscles to get themselves off the ground. These characters would also need to have very specific combination of wing size/shape to create the lift necessary to allow these humans to glide effectively.
The Incredible Hulk
The Incredible Hulk received his powers after having received a does of Gamma radiation. Gamma radiation is a form of electromagnetic radio nation that is more intense than X-rays. One blast of this would surely kill a character before it could give him super powers. However, the superhero industry has begun to consider this, and has begun to use alternative explanations to explain that way the many superheroes, like Spider-Man and the Hulk. Instead of radiation, or in the case of the Hulk radiation alone, genetic engineering is now responsible at least in part for these superheroes amazing powers.