Answer:
1. Luminosity
2.Apparent brightness
Explanation:
There are two factors on which brightness of star appear to be in the sky
The two factors are
1. Luminosity
2.Apparent brightness
1.Luminosity :It is defined as the total energy emitted by the object in a given time.Luminosity vary with the distance of observer from the star.Luminosity is a intrinsic property which depends on the fundamental chemical composition and structure of the material.Luminosity is depends on the size of star.Lager the star luminosity will be more.
2.Apparent brightness: It is defined as how bright a star appears from an observer on the earth and the amount of starlight reaching the earth.if the distance is large then the brightness decreases.When the distance of star from us small then the brightness of star increases.Distance is inversely proportional to brightness of the star.
Answer:
Explanation:
Given
mass of book(m)=2.1 kg
height up to which book is lifted is (h)2.2 m
height of person 
Potential energy of book relative to ground=mgh

(b)PE w.r.t to person head =mg(h-h0)

work done by person in lifting box 2.2 m w.r.t floor
Word done =Potential Energy of box relative to floor=45.2 J
The answer is most likely D. hope that helped

(E=mc^2)
<h3>
<u>Where</u><u>:</u></h3>
<u>m</u><u> </u><u>is mass</u>
<u>And c is a constant for speed of light</u>
Answer:


Explanation:
Given:
Let mass of the particle B be, 
then the mass of particle A, 
Energy stored in the compressed spring, 
Now when the compression of the particles with the spring is released, the spring potential energy must get converted into the kinetic energy of the particles and their momentum must be conserved.
Kinetic energy:

.............................(1)
<u>Using the conservation of linear momentum:</u>

.............................(2)
Put the value of
from eq. (2) into eq. (1)

...........................(3)
<u>Now the kinetic energy of particle B:</u>



Put the value of
form eq. (3) into eq. (1):

<u>Now the kinetic energy of particle A:</u>
<u />
<u />
<u />
<u />
