Abook with a mass of 2.0 kg is held in equilibrium on a board with a slope of 60.0° by a horizontal foce. what is the normal force exerted on the book?

When three forces are in equilibrium at a point, their ratios are the same as those of the corresponding lengths in a triangle formed from their three directions. 

I'll work in kg-equivalent-masses first, converting to N (Newtons) only at the end. 

The kg-equivalent forces are those of the weight due to a mass of 2.0 kg acting downwards (short "perpendicular side" of triangle), of 
2 sqrt(3) kg horizontally (long perp. side) and of 4.0 kg along the hypoteneuse, normal to the board.
(The ratios of these sides, 1sqrt(3)2 are the ratios for the 30, 60, 90 deg. triangle.) 

So the normal force exerted by the book is the force due to the weight of a 4.0 kg mass, that is
4.0 x 9.8 N = 
And the answer is
39 N. 
Have a nice day

Answer

the order for strong to weak forces such as

strong nuclear force → electromegnetic force → weak nuclear force → gravitational force

explanation

the fundamental forces are those forces that act between to objects or element to make interactions. there are four types of fundamental forces such as strong and weak nuclear forces (due to protons and electrons), electromagnetic force (due to the motion of electrons) and gravitational force (due to orbital movement of the planet). if these forces are arranged on the basis of their maximum strength then the order is

strong nuclear force → electromegnetic force → weak nuclear force → gravitational force

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