Some people are certainly less intelligent than others; some so gravely so that we may correctly classify them as stupid or even mentally retarded.
A dog runs out in front of a car and gets hit. Or a dog may run around some trees or bushes while wearing a long leash and get himself terribly tangled. We may call this dog stupid, and use that as an example of dogs being stupider than humans.
In parallel, one smarter human may see a second human doing something self-destructive that the first human would be smart enough not to do because the first human can predict the consequences while the second person doesn't see them coming quick enough like a bad chess player.
However, stupidity in that sense is only one reason people perform an action that a smarter person would know has a negative consequence. Other causes include addiction, masochism, apathy, gambling, compulsiveness, bad luck, misperception, mental disease, etc. For example, Vincent van Gogh was not a stupid man. Nonetheless, he cut off his ear which is an example not of an act of stupidity but rather of something else, perhaps insanity.
When the car is at the crest of the hill and moving at uniform speed there are two forces acting on it. One is the vertically downward force (f1) due to gravity, and a vertically upward force (f2) due to centrifugal force movement of the car along the circular path over the hill.
We calculate the downward gravitational force using the formula:
f1 = m*g = 1400*9.81 = 13734 N
Similarly, we calculate the upward centrifugal force using the formula:
f2 = m*(v^2)/r = 1400*(25^2)/210 = 4166.6667 N
The net force acting on the car is:
= f1 - f2 = 13734 - 4166.6667 = 9567.3333 N downward
Applied force on the car is 9567.3333 N downward.
Thunder makes a sound because of the constant pressure and sudden temperature change when it comes down to earth. Thunder is inside the lightening in a sense, it grows when air surrounds it. Lightning comes before thunder because the thunder needs time to reach down on earth to make the 'boom' sound.