(Solved): 3. A square thread power screw has an efficiency of 65% when raising a load. The coefficient of th ...

3. A square thread power screw has an efficiency of $$65\%$$ when raising a load. The coefficient of thread friction is $$0.15$$ with collar friction negligible. The pitch diameter of the screw is $$70\mathrm{mm}$$. When lowering the load, a uniform velocity is maintained by a brake mounted on the screw. If the load is 10 metric tons, what torque must the brake exert? (Ans: $$567.8\mathrm{N}?\mathrm{m}$$ )