Using a wavelength laser, you form the diffraction pattern of a wide slit on a screen. you measure on the screen that the dark fringe is away from the center of the central maximum. how far is the screen located from the slit?

y = λ   L/ a

Explanation:

The diffraction pattern of a single slit is side for the case of destructive interference by

     a sin  θ = m λ

Where a is the width of the slit, lm the wavelength and m an integer

In general the screen is much larger than the width of the spectrum, so the sine can approach the tangent

       sin  θ = tan θ = y / L

Substituting remains

       a y / L = m λ  

       y = m λ  L /a

For the first dark strip m = 1

      y = λ   L/ a

air exerts forces on falling objects near earth’s surface.

explanation:

the term 'free falls' refer to object that are falling towards the earth, in a situation in which gravity is the only force acting on the object.

for an object in free fall, the acceleration is constant (g, the gravitational acceleration), and so the velocity of the object constantly increases.

for objects near earth's surface, there is always another force acting on the object: the resistance due to the air. this force is opposed to the direction of fall of the object, and it is proportional to the velocity of the object, so as the object falls down, this force increases up to a point when it balances the force of gravity, and the object continues its motion at constant velocity (called terminal velocity). since in this case gravity is not the only force acting on the object, we are not in a situation of free fall.