Your Physics Book has a mass of 400 g. It is kept on a horizontal table. Taking g = 10 m/s², find the force (both magnitude and direction) exerted by

(a) the table on the Physics book (b) the Physics book on the table (c) the earth on the Physics book (d) the Physics book on the earth.

[here we neglect the mass of the table as it is not given]

the force exerted by the book and on the earth would be equal to the weight of the book, W = mg and

the force exerted on the book by the table sand the earth would be equal to the normal reaction force, N = mg (in magnitude)

so,

the weight of the book will be, W = mg = 0.4kg x 10m/s² = 4 N

now, the answers are

(a) 4 N upwards 

(b) 4 N downwards

(c) 4 N downwards 

(d) 4 N upwards