Please help me

5.02s    

Explanation:

Given parameters:

Initial speed  = 25m/s

Final speed  = 30m/s

Distance  = 138m

Unknown:

Time taken for the body to accelerate  = ?

Solution:

We start by finding the acceleration of the body using the expression below;

           v² = u² + 2as

v is the final velocity

u is the initial velocity

a is the acceleration

s is the distance

            30²  = 25²  + 2(a ) x 138

           900 = 625 + 276a

            900 - 625  = 276a

                275 = 276a

                   a = 0.996m/s²

Now to find the time taken, use the expression below;

            v  = u + at

t is the unknown time;

            30 = 25 + 0.996t

               5  = 0.996t

               t = 5.02s    

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

the answer is the first electromagnet (a). this is because it has more coils around the ferromagnetic material. increasing the number of coils increases the surface area in which the metal interacts with the current in the coil. this enables more atoms in the metal to become aligned hence becoming more magnetized.