Solve the following questions:
Question I: Calculate the pitch of a single-start square-thread of a jack which will just allow the load to fall uniformly under its own weight.
Question II: The mean diameter of the thread is 8 cm and coefficient of friction of 0.08. If the pitch is 15 mm, what is the torque required to lower a load of 3 kN?
Express your knowledge to solve the above questions, thanks.