Because dark line spectra result from passing white light through ionized gasses and plasmas, which is what the atmosphere of stars are made of. These frequencies are scattered by the star's atmosphere as it leaves the surface (photosphere) of the star, and don't make it to earth.
Answer:
1. Hydrogen
Atomic # = 1
Atomic Mass = 1.00794 ( If you round it it's 1.008 )
# of protons = 1
# of neutrons = none
# of electrons = 1
Answer:
This depends on the writers
if they want they can make spiderman deny the laws of nature
Answer:
Lever => 
Pulley => G = M x n (gravitational acceleration)
Wheel and axle => M.A = Radius of the wheel/radius of the axle = R/r
Inclined plane => It can be divided into two components: Fi = Fg * sinθ - parallel to inclined plane. Fn = Fg * cosθ - perpendicular one.