Answer:
a) F = 18.375N, b) F = 24.5 N
Explanation:
This exercise can be solved using the translational equilibrium equations.
Let's start by fixing a reference system with the horizontal x axis and the vertical y axis, from the statement of the exercise I understand that the wall is vertical and the book is supported on it, therefore the applied force is in the direction towards the wall
a) In this part the force that does not allow the movement of the book is requested, therefore the static friction coefficient must be used (μ_s = 0.8)
X axis
F - N = 0
N = F
Y axis
fr - W = 0
W = fr
where W is the weight of the book.
The friction force has the formula
fr = μ_s N
we substitute
mg = μ_s F
F =
let's calculate
F = 1.5 9.8 / 0.8
F = 18.375N
b) In this case the book is moving so the friction coefficient to use is kinetic ( μ_K = 0.6)
F =
we calculate
F = 1.5 9.8 / 0.6
F = 24.5 N
