Answer:
b) the refracted ray has an angle of 90 degrees
Explanation:
The angle of incidence is measured with respect to the normal separation of the media. The critical angle for total internal reflection occurs is:

Here  and
 and  are the refractive index of the mediums. This equation is an application of Snell's law, for the case where  the refracted ray has an angle of
 are the refractive index of the mediums. This equation is an application of Snell's law, for the case where  the refracted ray has an angle of  .
.
 
        
             
        
        
        
Answer:
35.3 N
Explanation:
U = 0, V = 0.61 m/s, s = 0.39 m
Let a be the acceleration.
Use third equation of motion
V^2 = u^2 + 2 as
0.61 × 0.61 = 0 + 2 × a × 0.39
a = 0.477 m/s^2
Force = mass × acceleration 
F = 74 × 0.477 = 35.3 N
 
        
             
        
        
        
Answer:
The distance traveled!
Explanation:
This is a velocity time graph of an object moving in a straight line due North. 
 
        
             
        
        
        
By 
vector addition.
In fact, velocity is a vector, with a magnitude intensity, a direction and a verse, so we can't simply do an algebraic sum of the two (or more velocities). 
First we need to decompose each velocity on both x- and y-axis (if we are on a 2D-plane), then we should do the algebraic sum of all the components on the x- axis and of all the components on the y-axis, to find the resultants on x- and y-axis. And finally, the magnitude of the resultant will be given by

where Rx and Rx are the resultants on x- and y-axis. The direction of the resultant will be given by

where 

 is its direction with respect to the x-axis.
 
        
        
        
Answer:
18 m/s
Explanation:
Given that,
Speed of river is 8 m/s due South 
From the shore, you see a boat moving South with a speed of 10 m/s. Both boat and river are moving in same direction. The resultant velocity will add up. 
v = 10 m/s + 8 m/s
v = 18 m/s
Hence, the rowers are moving with a speed of 18 m/s.