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:
when a two bodies A and B are moving at an angle 180° with each other then the relative velocity is the sum of bodies the velocity .i.e,
when the bodies move the opposite direction
then their relative velocity is the sum of individual velocities.
Answer:
1.38 x 10^-18 J
Explanation:
q = - 1.6 x 10^-19 C
d = 5 x 10^-10 m
the potential energy of the system gives the value of work done
The formula for the potential energy is given by

So, the total potential energy of teh system is

As all the charges are same and the distance between the two charges is same so the total potential energy becomes

K = 9 x 10^9 Nm^2/C^2
By substituting the values

U = 1.38 x 10^-18 J
The average speed is the distance per time ratio. velocity is the rate at which the position changes