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A hummingbird beats its wings up and down with a frequency of 100 Hz. What is the period of the hummingbirds flaps? (DO NOT INCLUDE UNITS IN
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If its history of, then b) because a) implies only present day (now)

Iwould have to say sorry i can't elaborate more. hope this though!

The boat's velocity relative to the riverbank can be resolved into two components. the component going north is 2.7 m/s and the component going west is 1.2 m/s.we add these two vectors and then find the magnitude of the resultant to get the speed.the magnitude of the resultant vector from adding can be obtained by the pythagorean theorem.    to two significant figures, the boat's speed relative to the riverbank is 3.0 m/s.