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15 Jan 2021
A man needs to travel from point A to point B, where point B is 
away, vertically opposite through the river, while the horizontal distance of point A to B is 
. The man needs to reach point B in minimum time. His speed on the ground is 
and in the water his speed is 
. Find the distance that the man will travel in the water when the travel time is at a minimum.
A man needs to travel from point A to point B, where point B is away, vertically opposite through the river, while the horizontal distance of point A to B is . The man needs to reach point B in minimum time. His speed on the ground is and in the water his speed is . Find the distance that the man will travel in the water when the travel time is at a minimum.
John David ManaloLv10
15 Jan 2021
be the velocity of light in air and 
the velocity of light in water. According to Fermat’s Principle, a ray of light will travel from a point A in the air to a point B in the water by a path ACB that minimizes the time taken. Show that
(the angle of incidence) and 
(the angle of refraction) are as shown. This equation is known as Snell’s Law.
, where s is measured in centimeters and t in seconds. (Take thepositive direction to be downward)