A horizontal ray travelling along +x strikes y²=8x and is reflected vertically upward. What is the x-coordinate of the point of incidence?
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A horizontal ray travelling along +x strikes y²=8x and is reflected vertically upward. What is the x-coordinate of the point of incidence?

G1 Physics · Accepted Answer

For y²=4ax, here a=2. The tangent slope is dy/dx=2a/y=4/y. For vertical upward reflection it must be +1, so y=4. Then 16=8x, giving x=2.