the figure below shows three masses connected to each other with strings. one of the masses sits on a table. the other two masses are hung off both sides of th etable from pulleys of negligibe mass. the masses of the blocks are m1= 3.5kg, m2=7.0 kg, and m3= 2.0kg and the masses of the strings are negligible. what is the smallest possible value of the static coefficient of friction between the middle block and the table