A can filled with water isrevolved in a vertical circle of radius 4 metre and the water just does no

In nonunifrom circular motion as in the above example the speed at highest point will be the least.

Now T 1/V

Let's imagine the above circular motion to be uniform circular motion with a constant speed as the least speed at the highest point.

The time period we found thus is 4 sec.

But actually the speed in the nonuniform motion is varying, and surely it's never less than the speed at the highest point, as a consequence we see that the average speed will be greater than the speed at the highest point.

This means the time period will be less than 4 sec. Well, we don't have much options with time period less than 4 sec, do we? 

Hence the only option and correct answer is 1 sec.

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Team,

TopperLearning.