This is what wiki says hope it helps
A displacement is a vector whose length is the shortest distance from the initial to the final position of a point P.[1] It quantifies both the distance and direction of an imaginary motion along a straight line from the initial position to the final position of the point.
A displacement may be also described as a 'relative position': the final position of a point (Sf) relative to its initial position (Si), and a displacement vector can be mathematically defined as the difference between the final and initial position vectors:
        
                    
             
        
        
        
a)
for the puck :
F = force applied in the direction of pull 
N = normal force on the puck in upward direction by the surface of table
W = weight of the puck in down direction due to force of gravity 
b)
along the vertical direction , normal force balance the weight of the puck , hence the net force is same as the force of pull F . 
so  F = ma                                    where m = mass of puck  , a = acceleration 
Fnet = F 
c)
since the net force acts in the direction of force of pull F , hence the puck accelerates in the same direction .
 
        
             
        
        
        
r₁ = distance of the point from the source = 43 km = 43000 m 
I₁ = intensity of earthquake wave at distance "r₁" = 2.5 x 10⁶ W/m² 
r₂ = distance of the point from the source = 1.5 km = 1500 m 
I₂ = intensity of earthquake wave at distance "r₂" = ?
we know that , for a constant power , the intensity of wave is inversely proportional to the distance from the source . 
I α 1/r²             where I = intensity of wave , r = distance from source
hence we can write 
I₁/I₂ = r₂²/r₁²
inserting the values 
(2.5 x 10⁶) /I₂ = (1500/43000)²
I₂ = 2.1 x 10⁹ W/m²
 
        
             
        
        
        
<span> the angle of reflection is 
30 degrees</span>