4. A skydiver is falling with speed v0 through the air. At that moment (time t = 0), she opens her parachute and experiences the force of air resistance whose strength is given by the equation F = kv, in which k is a proportionality constant and v is her descent speed. The total mass of the skydiver and equipment is m. Assume that g is constant throughout her descent. (a) Draw and label all the forces acting on the skydiver after her parachute opens. (b) Determine the skydiver’s acceleration in terms of m, v, k, and g. (c) Determine the skydiver’s terminal speed (that is, the eventual constant speed of descent). (d) Sketch a graph of v as a function of time, being sure to label important values on the vertical axis.

the displacement produced by the body.  

the amount of force subjected to the body.  

the angle between the direction of force and displacement

more than, less

less than, more

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

t = 1/400 h   ⇔ 0.0025 h ⇔ 9s ⇔ 0.15 m

any of the answers are correct.