Indian School Certificate – ( ISE BOARD )
Class – 11
Subject Wise Courses For Class – 11
Mathematics For Class 11
Physics For Class 11
Chemistry For Class 11
Biology For Class 11
Recommended Question & Answers for Class 11
1. Prove that cos x + cos (120° – x) + cos (120° + x) = 0.
LHS = cos x + cos (120° – x) + cos (120° + x)
= cos x + (cos 120° cos x + sin 120° sin x) + (cos 120° cos x – sin 120° sin x)
= cos x + 2 cos 120° cos x
= cos x + 2 cos x cos (90° + 30°)
= cos x + 2 cos x (- sin 30°)
= cos x + 2 x (1/2) cos x
= cos x – cos x
=0
2. Name the three classes of levers and state how are they distinguished. Give two examples of each class. ?
The following are the three classes of levers:
(i) Class I levers: In this type of the levers, the fulcrum F is in between the effort E and the load L. Example: claw hammer, beam of a physical balance, crowbar, a seesaw
(ii) Class 11 levers: In these type of levers, the load L is in between the effort E and the fulcrum F. Thus the effort arm is always longer than the load arm. Example: a wheel barrow, a paper cutter, a door, a nut cracker.
(iii) Class III levers: In these type of levers, the effort E is in between the fulcrum F and the load L. Thus the effort arm is always smaller than the load arm. Example: fishing rod
3. What would you observe when:
(b) Red litmus paper is introduced into a solution of ammonia in water
(c) Red litmus paper is introduced in Caustic soda solution?
Answer:
(a) Blue litmus will turn into red indicating the solution is acidic.
(b) No change will be observed.
(c) As caustic soda is basic in nature it will turn red litmus blue.