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Water and other liquid exerts --------when objective move through them

An object is placed at a certain depth from the upper surface of a liquid. When it is seen from air, it appears that the object is raised through (1)/(3) of the depth. Again if water is taken instead of the liquid it appears that the object is raised above through (1)/(4) of the real depth. Refractive index of liquid = (3)/(2) and refractive index of water = (4)/(3) . Explain the matter.

Fill in the blanks: Earth pulls every object towards itself through _____ force.

A concave mirror forms an image of an object, magnified 4 times. When the object is moved through 5 cm along the axis of the mirror, the magnification of the image is 5. What is the focal length of the mirror?

Two objects are thrown vertically upwards with the same velocity v from the same point. If the second object is thrown a time T later than the first object, when will the two objects collide with each other?

An object is placed in front of a concave mirror, a three times magnified image is formed. If the object is moved through a distance 20 cm towards the mirror, a virtual image of same magnification is formed. What is the focal length of the mirror?

Fill in the blanks: When an object is thrown upward, its speed ______ with altitude.

Two circles having radii r units interest each other in such a way that each of them passes through the centre of the other. Then the length of their common chord is ____

Comparatively, size of Li^o+ ion is very small with' respect to other alkali meta) ions but it moves through a solution less rapidly than the others. Justify