Poor Dolly’s T.V. has only 4 channels, all of them quite boring. Hence it is not surprising that she desires to switch (change) channel after every one minute. Then find the number of ways in which she can change the channels so the she is back to her original channel for the first time after 4 min.

Read the following passage and answer the questions that follow Rahini and her parents were waching a televison programme . An advertisement flashed on the screen which was promoting use of sanitary napkins . Rahini's parents suddenly changed the channel , but she objected to her parents and explained the need and importance of such advertisment . Do you think that Rahini's objection towards her parents was correct ? If so , why ?

Read the following passage and answer the questions that follow Rahini and her parents were waching a televison programme . An advertisement flashed on the screen which was promoting use of sanitary napkins . Rahini's parents suddenly changed the channel , but she objected to her parents and explained the need and importance of such advertisment . What is first menstruation called ? when does it occur?

Two friends A and B (each weighing 40 kg ) are sitting on a frictionless platform some distance d apart. A rolls a ball of mass 4 kg on the platform towards B which B catches. Then B rolls the ball towards A and A catches it. The ball keeps on moving back and forth between A and B . The ball has a fixed speed of 5 m//s on the platform. a. Find the speed of A after he rolls the ball for the first time. b. Find the speed of A after he catches the ball for the first time. c. Find the speed of A and B after the ball has made five round trips and is held by A . d. How many times can A roll the ball? e. Where is the centre of mass of the system A + B + ball at. the end of the nth trip?