Christopher can paddle a canoe in still water at 8 km/h. how successful will he be at canoeing upstream (against the current) in a river that flows at 8 km/h?

Christopher will not make any progress upstream. From the point of view of his friends standing on the riverbank, he'll remain at one point, motionless except for his furious paddling motions.

Given data:

The speed of Christopher in still water is, v = 8 km/h.

The speed of river is, u = 8 km/h.

The upstream is the motion of any object (say boat) in a river, which is in the direction opposite to the direction of flow of stream or river. And the expression for the upstream as per the given problem is,

upstream = v - u

So, on substituting the values we get,

upstream = 8 - 8

upstream = 0 km /h.

Thus, we can conclude that Christopher will not make any progress upstream. From the point of view of his friends standing on the riverbank, he'll remain at one point, motionless except for his furious paddling motions.

Learn more about the upstream here:

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conservation of mass

mass before something happens = mass afterwards