I used to teach physics 101. Lots of people fail. For many people, even people who can easily do the algebra it requires, physics is just not intuitive. You can try to explain it a hundred ways, but its a lost cause for many.
Really? Physics might not be the most intuitive of things, but personally, I find languages worse than physics. And is it just me, but isn't physics 101 (or in my case, high school physics in class 1, 2 and 3) just one big exercise in finding the correct formula and filling in the correct values?
You would be surprised by how many people have difficulty with the plug-the-numbers-into-the-formula type of work. The major problem many students have is in identifying what the correct formula to apply is. Typically in algebra-based intro to physics the hardest any problem is going to be is two equations and two unknowns, algebra that should have been learned in early high school. But even if the algebra isn't a problem, getting some students to recognize which variable stands for what physical entity is sometimes harder than it should be. Maybe it is one of the downsides of letting everybody into college in the US. There are a lot of upsides to that, too, but its certainly a two sided coin.