1. Repeat problem 12-7 if everything remains the same except that the power screw has double square threads.

2.A 40-mm rotating power screw with triple square threads has a pitch of . The screw is to be used to lift a 22 kN load at a speed of 4 m/min. Friction coefficients for both the collar and threads have been determined to be . The mean thrust collar friction diameter is 70 mm. Determine the power required to drive the assembly.

3. Find the torque required to drive a 16-mm single-start square thread power screw with a 2 mm pitch. The load to be lifter is 3.6 kN. The collar has a mean friction diameter of 25 mm, and the coefficients of collar and thread friction are mc = 0.12 .