Correct Answer : Option (B) : W/Ï€dtz
Explanation : At root of threads, the area parallel to direction of force is considered which is equal to circumference x thickness x no. of threads.
Correct Answer : Drums with helical grooves
Explanation : They have more bearing surface of the drum and prevent friction between adjacent turns of the rope.
Correct Answer : Increasingly centrifugal force in large sheaves
Explanation : Larger sheaves have higher centrifugal forces and higher cost because more material is used in their construction.
Correct Answer : Both bending and tensile stress
Explanation : There is direct tensile stress due to load being raised as well as bending stress.