The Rotating Watch

Classical Mechanics Level 1

A watch is set on a horizontal table. When the second's hand comes at 12, the watch is set into rotation in the counter-clockwise direction such that the second's hand appears to be stationary (to an observer looking at the watch from above).

How many rotations will the watch make(with respect to the stationary observer) in the time taken for the earth to rotate once?

Additional information: - Time taken by the Earth to complete a rotation is about 86,400 seconds.

Data Insufficient 720 1,440 1 3600

Anshul Agrawal by Anshul Agrawal , 20, India

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1 solution

Arjen Vreugdenhil
Nov 29, 2017

The number of rotations of the watch relative to the second hand is equal to the number of rotations of the second hand relative to the watch.

Since the second hand rotates once in a minute, the answer is the number of minutes in a day: 24 × 60 = 86 400 60 = 1440 24\times 60 = \frac{86\:400}{60} = \boxed{1440} .

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