An elevator with a person inside is traveling upwards at a velocity of +5 m/s and accelerating downward with an acceleration of -4 m/s^2. Draw a Free-Body
Diagram showing the forces acting on the person. Is the speed of the person is
increasing, decreasing, or constant?
increasing
O decreasing
O constant
O constant

At this precise moment, the person's speed is decreasing.

3. dark matter

empty space could also be a simple vacuum

you'd use the equation that establishes a relationship between  energy  and  wavelength, which looks like this

e=h⋅cλ, where

λ  - the wavelength of the photon; c  - the speed of light, usually given as  3⋅108m/s; h  -  planck's constant, equal to  6.626⋅10−34j s

plug the value you were given for the energy of the photon in the above equation to get the wavelength

e=h⋅cλ⇒λ=h⋅ce

λ=6.626⋅10−34js⋅3⋅108ms−1.257⋅10−24j=1.581⋅10−1m