A force of 36.0 N is required to start a 3.0-kg box moving across a horizontal concrete floor. Part A) What is the coefficient of static friction between the box and the floor? Express your answer using two significant figures. Part B) If the 36.0-N force continues, the box accelerates at 0.54 m/s^2. What is the coefficient of kinetic friction? Express your answer using two significant figures.

Respuesta :

Answer:

A) 1.2

B) 1.1

Explanation:

A)

F = force required to start the box moving = 36.0 N

m = mass of the box = 3 kg

[tex]F_{g}[/tex]  = weight of the box = mg = 3 x 9.8 = 29.4 N

[tex]F_{n}[/tex]  = normal force acting on the box by the floor

normal force acting on the box by the floor is given as

[tex]F_{n}[/tex]  = [tex]F_{g}[/tex] = 29.4

[tex]F_{s}[/tex]  = Static frictional force = F = 36.0 N

[tex]\mu _{s}[/tex] = Coefficient of static friction

Static frictional force is given as

[tex]F_{s}[/tex]  = [tex]\mu _{s}[/tex] [tex]F_{n}[/tex]

36.0  = [tex]\mu _{s}[/tex] (29.4)

[tex]\mu _{s}[/tex] = 1.2

B)

a = acceleration of the box = 0.54 m/s²

F = force applied = 36.0 N

[tex]f_{k}[/tex] = kinetic frictional force

[tex]\mu _{k}[/tex] = Coefficient of kinetic friction

force equation for the motion of the box is given as

F - [tex]f_{k}[/tex] = ma

36.0 - [tex]f_{k}[/tex] = (3) (0.54)

[tex]f_{k}[/tex] = 34.38 N

Coefficient of kinetic friction is given as

[tex]\mu _{k}=\frac{f_{k}}{F_{n}}[/tex]

[tex]\mu _{k}=\frac{34.38}{29.4}[/tex]

[tex]\mu _{k}[/tex] = 1.1