If you jump barafooted on a hard surface, your legs get injure. But they are not injured if you jump on a soft surface like sand or pillow. Explain.

Can we get out of smooth surface by taking jump on it ?

Consider the following statement. When jumping from some height, you should bend your knees as you come to rest instead of keeping your legs stiff. Which of the following relations can be useful in explaining the statement?

One hard and stormy night you find yourself lost in the forest when you come upon a small hut. Entering it you see a crooked old woman in the corner hunched over a crystal ball. You are about to make a hasty exit when you hear the howl of wolves outside. Taking another look at the gyspy you decide to take your chances with the wolves, but the door is jammed shut. Resigned to a bad situation you approach her slowly, wondering just what is the focal length of that nifty crystal ball. The old lady moves the crystal ball closer to her wrinkled old face. At some point you can no longer get an image of her . At what object distance will there be no change of the gypsy formed?

Consider a 20 W bulb emitting light of wavelength 5000 Å and shining on a metal surface kept at a distance 2m.Assume that the metal surface has work function of 2eV and that each atom on the metal surface can be treated as a circular disk of radius 1.5 Å. (i)Estimate no. of photons emitted by the bulb per second.[Assume no other losses] (ii)Will much time would be required by the atomic disk to receive energy equal to work function (2eV)? (iv)How many photons would atomic disk receive within time duration calculated in (iii)above? (v) Can you explain how photoelectric effect was observed instantaneously?

The Sun is a hot plasma (ionized matter) with its inner core at a temperature exceeding 10^(7)Kg , and its outer surface at a temperature of about 6000K. At these high temperatures , no substance remains in a solid or liquid phase. In what range do you expect the mass density of the Sun to be, in the range of densities of solids and liquids or gases ? Check if your guess is correct from the following data: mass of the Sun =2.0xx10^(30)Kg , radius of the Sun =7.0xx10^(8)m .

A corn cob (see the given figure), shaped somewhat like a cone, has the radius of its broadest end as 2.1 cm and length (height) as 20 cm. If each 1 cm^(2) of the surface of the cob carries an average of four grains, find how many grains you would find on the entire cob.