Plate tectonics<span>is a </span>scientific theory<span> that describes the large-scale motion of </span>Earth<span>'s </span>lithosphere<span>. This theoretical model builds on the concept of </span>continental drift<span> which was developed during the first few decades of the 20th century. The </span>geoscientific<span> community accepted plate-tectonic theory after </span>seafloor spreading was validated in the late 1950s and early 1960s.<span>The lithosphere, which is the rigid outermost shell of a planet (the crust and upper mantle), is broken up into </span>tectonic plates<span>. </span>
        
             
        
        
        
The gravitational potential energy of the object is 100 J.
Gravitational potential energy stored in an object is the work done in raising the object to a height <em>h</em> against the gravitational force acting on it.
The gravitational force acting on a body is its weight mg, where m is its mass and g, the acceleration due to gravity.
Work done by a force is equal to the product of the force and the displacement made by the point of application of the force.

The weight of the object is given as 20 J and it is raised to a height of 5 m.

The gravitational potential energy of the object is 100 J.
 
        
                    
             
        
        
        
Answer:
1). 
2). Toward us
3). 
4). Toward us
5). 
6).  Away from us
7). 
8). Away from us
Explanation:
Spectral lines will be shifted to the blue part of the spectrum if the source of the observed light is moving toward the observer, or to the red part of the spectrum when it is moving away from the observer (that is known as the Doppler effect).
The wavelength at rest is 121.6 nm ( )
)

 
 
Then, for this particular case it is gotten:
Star 1: 
Star 2:  
 
Star 3:  
 
Star 4:  
 
Star 1:
 
 
Toward us
Star 2:
 
 
Toward us
Star 3:

Away from us
Star 4:

Away from us
Due to that shift the velocity of the star can be determine by means of Doppler velocity. 
 (1)
  (1) 
Where  is the wavelength shift,
 is the wavelength shift,  is the wavelength at rest, v is the velocity of the source and c is the speed of light.
 is the wavelength at rest, v is the velocity of the source and c is the speed of light.
 (2)
  (2)
<em>Case for star 1  :</em>
:</em>
<em></em>
 
 
 
 
Notice that the negative velocity means that is approaching to the observer. 
<em>Case for star 2  :</em>
:</em>
 
 
 
 
<em>Case for star 3  :</em>
:</em>
 
 
 
 
<em>Case for star 4  :</em>
:</em>
 
 
 
 
 
        
             
        
        
        
<h2>A is the correct answer!</h2><h3></h3><h3>I'm too lazy to explain :(</h3><h3></h3><h3><em>Please let me know if I am wrong.</em></h3>