Aman pushes horizontally on a desk that rests on a rough wooden floor. the coefficient of static friction between the desk and floor is 0.750 and the coefficient of kinetic friction is 0.600. the desk's mass is 100 kg. he pushes just hard enough to get the desk moving and continues pushing with that force for 5.00 s. how much work does he do on the desk? work = answer j

m = mass of desk = 100 kg

g = acceleration due to gravity = 9.8 m/s²

μ = coefficient of static friction = 0.6

F = applied force

force required to start the desk moving must be greater than or equal to static frictional force

F = static frictional force

F = μ mg

inserting the values

F = (0.750) (100 x 9.8)

F = 735 N

μ' = coefficient of kinetic friction = 0.6

once the mass starts moving , kinetic frictional force acts on it , which is given as

f' = μ' mg

a = acceleration of the mass

for the desk , force equation is given as

F - f' = ma

μ mg - μ' mg = ma

a = (μ - μ') g

a = (0.750 - 0.600) (9.8)

a = 1.47 m/s²

v₀ = initial velocity of desk = 0 m/s

t = time of travel for desk = 5.00 s

d = displacement of the desk = ?

using the equation

d = v₀ t + (0.5) a t²

d = (0) (5) + (0.5) (1.47) (5)²

d = 18.375 m

work done by man is given as

W = F d

W = (735) (18.375)

W = 13505.625 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