In November of 1940, the newly-constructed bridge over the Tacoma Narrows strait

Question

In November of 1940, the newly-constructed bridge over the Tacoma Narrows strait collapsed after undergoing severe oscillations brought on by strong winds. As seen in the video, the oscillations partly took the form of a torsional (twisting) standing wave. A node of the standing wave can be seen near each of the two tall towers, with another about halfway between the towers. The wavelength of the standing wave is therefore approximately equal to the distance between the towers, which was about 850 m. The time for one complete oscillation was observed to be about 4.5 s. Using these observations, calculate the approximate speed of the torsional wave on the bridge.

Explanation / Answer

from the given data

wavelegth, lamda = 850 m

Time period, T = 4.5 s

we know,
frequency, f = 1/T

= 1/4.5

= 0.2222 hz

we know, wave speed v = lamda*f

= 850*0.2222

= 189 m/s <<<<<<---------------Answer

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