# KVPY Interview Important Questions Physics Part 4

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Q: 27. What is escape speed

Sol. Minimum speed of the particle at a point so that particle at a point inside the gravitational filed so that it move up to infinite (i.e.. , outside field at the planet)

Q: 28. What is the value of escape speed from earth՚s surface

Sol.

Q: 29. What will happen if we project a rocket towards the ground?

Sol. It will collide with earth and explode

Q: 30. Where does the energy lost in the above collision goes?

Sol. In the form of sound, Heat, electromagnetic radiation, Elastic potential energy in the form of deformation of the material of rocket i.e.. , explosion

Q: 31. What will happen if the collision is completely inelastic?

Sol. In completely elastic collision maximum energy lost takes place and no elastic reformation produce in material after deformation

i.e.. , no relative velocity of separation produce along the line at impact.

Q: 32. Derive the expression for rocket propulsion

Sol. Let be the mass of the rocket at time t = 0. Its mass at any time t and v its velocity at that moment. Initially, let us suppose that the velocity of the rocket is u.

Further, let be the mass of the gas ejected per unit time and the exhaust velocity of the gases with respect to rocket. Usually and are kept constant throughout the journey of the rocket. Now, let us write few equations, which can be used in the problems of rocket propulsion. At time t = t,

1.

2.

3.

4. Net acceleration of the rocket

Or

Or

Or

Thus, … (i)

Q: 33. How energy is generated in the sun?

Sol. It is due to nuclear reaction (function of hydrogen) in core of sun.

Q: 34. What is mass defect

Sol. It has been observed that there is a difference between expected mass and actual mass of a nucleus.

Q: 35. How was it found out that sun contains hydrogen?

Sol. With the help of spectrum of radiation coming from the sun gives the idea of element on sun.

Q: 36. What is spectrum?

Sol. It is an arrangement of E. M. W. on a scale in increasing ‘λ’ is visible spectrum.

Q: 37. What are the different kinds of spectrum?

Sol. Absorption and emission spectrum

Q: 38. What is the difference between emission and absorption spectrum?

Sol. Emission spectrum: Spectrum with the all radiations, which is emitted by the atom.

Absorption spectrum: Spectrum with all the radiations which is absorb by the atom when radiations passes through the material i.e.. , spectrum with missing line in radiation.

Q: 39. How is spectrum generated?

Sol. When radiations absorb or emitted by the elements, then spectrum is produce which can be studied by spectrum-eter

Q: 40. Whether the spectrum obtained from sun emission or absorption spectrum?

Sol. Spectrum of radiation emitted by the core of sun is emission spectrum and it is observed at the surface of earth as a absorption spectrum because radiations are absorb by the atmospheric gases.

Q: 41. What is Fraunhofer spectrum?

Sol. Absorption Spectrum of sun is called Fraunhofer spectrum.

Q: 42. Why does Gauss՚ Law consider charges only inside the imaginary closed surface, and not the ones outside?

Sol. Because solid angle subtended by a point outside of a closed surface is always zero.

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