The horizontal surface on which the objects slide is frictionless. The acceleration of gravity is 9.8 m/s2. block 1 is 1kg block 2 is 9kg block 3 is 4kg from left to right. If Fl = 20 N and Fr = 7 N, what is the magnitude of the force exerted on the block with mass 9 kg by the block with mass 4 kg? Answer in units of N.

The space between two 15-in.-long concentric cylinders is filled with glycerin (viscosity = 8.5 × 10-3 lb·s/ft2). the inner cylinder has a radius of 1 in. and the gap width between cylinders is 0.1 in. determine (a) the torque and (b) the power required to rotate the inner cylinder at 180 rev/min. the outer cylinder is fixed. assume the velocity distribution in the gap to be linear.