The method by which the massive lintels (top stones) were lifted to the top of the upright stones at Stonehenge has long been debated. One possible method was tested in a small Czech town. A concrete block of mass 5124 kg was pulled up along two oak beams whose top surfaces had been debarked and then lubricated with fat (Figure). The beams were 10 m long, and each extended from the ground to the top of one of the two upright pillars onto which the block was to be raised. The pillars were 3.9 m high; the coefficient of static friction between block and beams was 0.22. The pull on the block was via ropes wrapped around it and around the top ends of two spruce logs of length 4.5 m. A platform was strung at the opposite end of each log. When enough workers sat or stood on a platform, the attached spruce log would pivot about the top of its upright pillar and pull one end of the block a short distance up a beam. For each log, the rope holding the block was approximately perpendicular to the log; the distance between the pivot point and the point where the rope wrapped around the log was 0.70 m. Assuming that each worker had a rnass of 85 kg, find the smallest number of workers needed on the two platforms so that the block begins to move up along the beams. (About half this number could actually move the block by moving first one end of it and then theother.)

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0.70 m -4.5 m Block- Spruce - log 3.9 m 10 m Worker - Platform- Pillar Oak beam