What if the computer is not fast enough to run at frequency 50?
If a computer can't update logic at 50 times a second, then it's nothing more than a glorified calculator. Basically, it would have to be a seriously slow computer if it can't. The logic cycle should take anywhere from less than a millisecond to a few milliseconds, depending on the amount of work being done. It's the actual rendering that takes time.
My current project's logic cycle takes anywhere between 0 and 1 millisecond, with the rendering on my system taking between 2-3 millisecs. I have the logic updating at 200 times per second and the game runs just fine on all of the systems in my sig, plus a slower, 6 year old PC that I also test stuff out on.