If the bridge was supported by and roatated about at its end B, would the same t
ID: 2077103 • Letter: I
Question
If the bridge was supported by and roatated about at its end B, would the same torque open the bridge in the same time, or would it open slower or faster? What are the benefits of making the bridge with the variable depth structure shown.
1. A swing bridge opens and closes by turning, using a motor located at A under the center of the deck that applies a torque M to the bridge. If the bridge was supported by and rotated about at its end B, would the same torque open the bridge in the same time, or would it open slower or faster? What are the benefits of making the bridge with the variable depth (thickness) substructure shown?Explanation / Answer
As the moment of inertia increases when the axis of rotation is being shifted towards the end so more time is needed to open the bridge with the same torque. The bridge would open slower.
As the bridge gets lighter around the two ends due to less depth, the moment of inertia becomes less than a bridge with constant depth. This results a quicker opening of the bridge as the same amount of torque has to do less work. This makes the whole structure efficient.
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