A horizontal plane supports a plank with a bar of mass m=1 kg placed on it and attached light elstic cord of length l=40cm to a point O . Coefficient of friction b/w bar and plank equals k=0.20.The plank is slowly shifted to right until the bar starts sliding over it . It occurs at the moment when cord deviates from vertical by an angle θ=30°.Find the work that has been performed by that moment by the friction force acting on the bar in the reference frame fixed to the plane
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UP 0 DOWN 0 0 0
