Two students are messing around with a nerf gun during a fire drill. they manage to fire a foam dart directly upwards from an inital height of 1.5 m above the ground. four seconds later, the foam dart hits the ground. what was the initial velocity of the dart?

v₀= 19.23 m/s

Explanation:

Look at the attached graphic

Foam dart Kinematic 1-2 (upward movement), vf₂=0 ,

We calculate t₁ and y₁ to reach the highest point (2)

vf₂=v₀-gt₁  

t₁=v₀/g

v f₂²=v₀²-2g*y₁

2g*y₁ =v₀² , y₁=v₀²/2g

Foam dart Kinematic 2-3 (downward movement), v₀₂=0 ,

We calculate t₂ and y₂ from the highest point (2) to

touch the ground (3)

vf₃=v₀₂+gt₂   , v₀₂=0

gt₂=vf₃ , t₂=vf₃/g

vf₃²=v₀₂²+2g*y₂

y₂= 1.5+y₁

y₂= 1.5+v₀²/2g

We propose the equation for the total time (Four seconds) :

t₁ = time it takes from position 1 to position 2 (going up)

t₂: and time that takes from position 2 to position 3 ( going down)

t₁+t₂=4

v₀/g+ vf₃/g =4

v₀ + vf₃ =4g

 : we move v to the other side and square both sides of the equation

v₀²+29.4=(4g-v₀²)²

v₀²+29.4=(4g)²-8gv₀+v₀² we eliminate v₀²

29.4=(4g)²-8gv₀

8*g*v₀=(4*g)²-29.4

v₀=1507.24/78,4

v₀= 19.23 m/s

i don't know that i agree with that but what's the question ?

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