Correct Answer : Option (C) : Resistance in the middle
Explanation : In a bottle opener fulcrum can be considered at the end and resistance in middle as the actual work is done on the bottle cap which lies in middle of opener.
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.