Correct Answer : Option (B) : 50%
Explanation : For self locking screw Ǿ(friction angle)>á¼€ (helix angle), hence efficiency < tanǾ/tan(Ǿ+á¼€) or efficiency < tanǾ(1-tan²Ç¾)/2tanǾ.
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.