Question

how do we determine the force exerted by books on a bookcase

Answer 1

thats physics

Answer 2

do you know how many forces are acting on the books?

Answer 3

there are two forces, normal force and the gravity, normal force pushing up and gravity pushing down which is why the book is at rest, its not moving they cancel out each other

Answer 4

F=ma

Answer 5

in this case, a would be gravity

Answer 6

you can probably do the rest just plug it in, you can rearrange the formula if needed, good luck :D