1. A rectangular block is at rest on a rough horizontal surface. A string is attached to one end of the block. You pull on the string (parallel to the surface) and the block does not move. Draw a free body-diagram to show all the forces acting on the block and use the relative size of your arrow vectors to represent the magnitude. Label all forces. How do the magnitudes of the forces compare to each other? 2. Describe how the forces you identified in number 1 are changed for the block when it moves with constant velocity. Draw a free body diagram and label the forces and use the relative size of your arrows to represent the magnitude.

3. Explain why in Part III, you simply get the mean value of the limiting angles of repose without considering that there are 5 different sets of masses?