The phenomenon of physics that deals with the constitution and structure of matter at the minute scales of atoms and nuclei is

If the length of a rod is measured as 830600 mm , then the number of significant figures in the measurement is

A particle initially at rest is moving along a straight line with an acceleration of $2 \mathrm{~ms}^{-2}$. At a time of 3 s after the beginning of motion, the direction of acceleration is reversed. The time from the beginning of the motion in which the particle returns to its initial position is

If a body projected with a velocity of $19.6 \mathrm{~ms}^{-1}$ reaches a maximum height of 9.8 m , then the range of the projectile is

(Neglect air resistance)