## Wednesday, 16 October 2013

### CBSE Class 9th Science | Chapter 12. Sound | | Solved Exercises

Question 1. What is sound and how is it produced?
Answer. Sound is a form of energy which produces a sensation of hearing in our ears.Sound is produced due to vibration of different objects and needs a material medium for its propagation. Sound travels as a longitudinal wave through a material medium by creating a series of successive compressions and rarefactions . In sound propagation, it is the energy of the sound that travels and not the particles of the medium. We can produce sound by plucking, scratching, rubbing, blowing or shaking different objects

## Saturday, 5 October 2013

### CBSE Class 9th | Science | Chapter 11. Work And Energy | Solved Exercises

Intext Questions | Page 148 | Chapter 11. WORK AND ENERGY| CBSE Class 9th  Science

Question 1. A force of 7 N acts on an object. The displacement is, say 8 m in the direction of the force. Let us take it that the force acts on the object through the displacement. What is the work done in this case ?
Answer. Work done (W) on an object is equal to the product of magnitude of the force (F) and the distance moved by the body (s) in the direction of the applied force
Work done (W) = Force(F) × Displacement (s)
∴ W = 7 N × 8 m = 56 J