Question

A 2.03 kg book is placed on a flat desk. Suppose the coefficient of static friction between the book and the desk is 0.442 and the coefficient of kinetic friction is 0.240. How much force is needed to begin moving the book?
How much force is needed to keep the book moving at constant speed once it begins moving?

Answer 1

Answer:

a) 8.80 N

b) 4.78 N

Explanation:

The weight of the book is

$W = mg = 2.03\times9.81 = 19.9143 \text{ N}$

By Newton's third law, the reaction from the table, R, is equal to its weight.

R = 19.9143 N

From the law of solid friction,

$F = \mu R$

F is the maximum frictional force and $\mu$ is the coefficient of friction.

a) The force needed to begin moving the book is that needed to overcome static friction

$F = 0.442\times19.9143 = 8.80\text{ N}$

b) The force needed to move the book at constant speed once it begins moving is that needed to overcome kinetic friction

$F = 0.240\times19.9143 = 4.78\text{ N}$