A uniform disk of radius 0.2 m and mass m = 16 kg is mounted on a nearly frictionless axle. A string is wrapped tightly around the disk and pulled with a constant force of F = 1 N. After a while the disk has reached an angular speed of !0 = 1.2 rad/s. What is its angular speed 1.5 s later?

ω = 2.13rad/s

Explanation:

Given

F = 1N = force applied, m = 16kg, R = 0.2m

ωo = 1.2rad/s

t = 1.5s

ω = ?

Where

α = angular acceleration

ωo = initial angular speed

And ω = angular speed at a later time t

For a rigid body rotating about an axis

τ = FR= I×α

I = 1/2×MR² for a uniform disk

FR = (1/2×mR²)×α

= 1/2×mR²×(ω – ωo)/t

Therefore

FR= 1/2×mR²×(ω – ωo)/t

2Ft/mR = ω – ωo

ω = 2Ft/mR + ωo

ω = 2×1×1.5/(16×0.2) + 1.2 = 2.13 rad/s

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