Aboy pulls a 30.0-kg box with a 210-n force at 39° above a horizontal surface. if the coefficient of kinetic friction between the box and the horizontal surface is is 0.23 and the box is pulled a distance of 38.0 m, what is the work done by the friction force on the box?

W= - 1414.48 J  : Work done by the friction force on the box.

Explanation:

Work concept

The work (W) of a given force is defined as the product of the force (F) by the distance(d) in which the force acted.

W= F*d :in (Joules)  Formula (1)

Friction force concept

Ff=μk*N  Formula (2)

μk=coefficient of kinetic friction

N= Normal force

We apply Newton's first law for forces in the direction of the axis y

∑Fy=0 Equation (1)

The forces acting on the box in the direction of the axis and are the following:

We apply equation (1) and do the algebraic sum of forces in y

Fy+N-W=0

132.16+N-294=0

N= 294-132.16=161.84 N

We apply formula (2) to calculate Ff:

Ff= -0.23*161.84=-37,22N  The frictional force is negative because it goes in the opposite direction to the displacement.

We apply formula (1) to calculate the work done by the friction force on the box

W= - 37,22 N * 38 m = -1414.48 N*m = -1414.48 J

electromagnetic shielding is the practice of reducing the electromagnetic field in a space by blocking the field with barriers made of conductive or magnetic materials. shielding is typically applied to enclosures to isolate electrical devices from their surroundings, and to cables to isolate wires from the environment through which the cable runs. electromagnetic shielding that blocks radio frequency electromagnetic radiation is also known as rf shielding.

the shielding can reduce the coupling of radio waves, electromagnetic fields and electrostatic fields. a conductive enclosure used to block electrostatic fields is also known as a faraday cage. the amount of reduction depends very much upon the material used, its thickness, the size of the shielded volume and the frequency of the fields of interest and the size, shape and orientation of apertures in a shield to an incident electromagnetic

from wikipedia

conservation of mass

mass before something happens = mass afterwards