A person holds a bundle of hay over his head for 30 minutes and gets tired. Has he done some work or not,? Justify your answer.

What is the work done by the force of gravity on a satellite moving round the earth ? Justify your answer.

A coolie is walking on a railway platform with a load of 30 kg on his head. How much work is done by coolie?

A cyclist after travelling a certain distance stopped for 30 minutes to repair the cycle. Then he completed the whole journey of 30 km at half speed and took a total time of 5 hours. If the breakdown has occurred 10 km further off, he would have completed the whole journey in 4 hours. Find where the breakdown occurred and his original speed.

A person is trying to push a box, the whole day he makes use of his stored energy but cannot move it. In physics we say he has not done any work. Explain why?

Answer the following :- In Fig. 6.13(i) the man walks 2 m carrying a mass of 15 kg on his hands. In Fig. 6.13(ii), he walks the same distance pulling the rope behind him. The rope goes over a pulley, and a mass of 15 kg hangs at its other end. In which case is the work done greater ?

Raman went to a hospital with his father to see his uncle who was admitted there because of some health problems. The doctor asked Raman to bring a particular injection to be given to his uncle. When Raman brought the injection, the doctor asked him to get the injection changed from the chemist. Raman insisted that it was the same injection as prescribed by him and its expiry date is also next year. But the doctor explained Raman that the injection has not been expired but it was not of compatible concentration as prescribed by him. Raman felt satisfied and got the injection changed Answer the following questions: What was the reason for asking Raman to get hte injection of compatible concentration?

classically an electron can be in any orbit around nucleus of an atom. Then what determines the typical atomic size? Why is an atom not, say, thousand times bigger than its typical size? Thequestion had greatly puzzled Bohr before he arrived at his famous model of the atom that you have learnt in the text. To simulate what he might well have done before his discovery, let us play as followswith the basic constants of nature e, me, c and see if we can get a quantity with the dimensions of length that is roughly equal to the known size of an atom (~ 10 m).- You will find that the length obtained above is many orders of magnitude smaller than the atomic dimensions. Further, it involves c. But energies of atoms are mostly in non-relativistic domain where c is not expected to play any role. This is what may have suggested Bohr to discard c and look for else h had already made its appearance elsewhere. Bohr lay in recognising that h, m_e , and e will yield the right atomic size. Construct a quantity with the dimension of length from h, me, and e and confirm that its numerical value has indeed the correct order of magnitude.

In your neighbourhood a person was appearing weak. His family members asked you the possible reason. You adviised him to consulrt doctor which appear to be some metabolic disorder. Name the hormones the deficiency of which has caused these disorders.