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The 4.00-kg block in the figure (Figure 1)is attached to a vertical rod by means of two strings. When the system rotates about the axis of the rod, the strings are extended as shown in the diagram and the tension in the upper string is 81.0 N. What is the tension in the lower cord? How many revolutions per minute does the system make? Find the number of revolutions per minute at which the lower cord just goes slack. 1.25 m 2.00 m 4.00 kg 1.25 m