A 1-kg book is at rest on a desk. Determine the force the desk exerts on the book
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General Formulas and Concepts:

Math

Pre-Algebra

Order of Operations: BPEMDAS

BracketsParenthesisExponentsMultiplicationDivisionAdditionSubtractionLeft to Right

Physics

Forces

SI Unit: Newtons N

Free Body Diagrams

Gravitational Force:

m is mass (in kg)g is Earth's gravity (9.8 m/s²)

Normal Force:

Newton's Law of Motions

Newton's 1st Law of Motion: An object at rest remains at rest and an object in motion stays in motionNewton's 2nd Law of Motion: F = ma (Force is equal to [constant] mass times acceleration)Newton's 3rd Law of Motion: For every action, there is an equal and opposite reactionExplanation:

Step 1: Define

1 kg book at rest

Step 2: FBD

See Attachment

Draw a free body diagram to label the forces acting upon the book. We see that we would have gravitational force from Earth pointing downwards and normal force from the surface of the desk pointing upwards.

Since the book is not moving, we know that ∑F = 0 (sum of forces equal to 0).

Step 4: Find Normal Force

Define Forces [Newton's Law of Motions]:                                                 [Newton's Law of Motions] Substitute in forces:                                         [Newton's Law of Motions] [Addition Property of Equality] Isolate :     [Newton's Law of Motions] Substitute in :                                               [Newton's Law of Motions] Rewrite:                                                             [Newton's Law of Motions] Substitute in variables:                                   [Newton's Law of Motions] Multiply: