Q.Explain what is meant by a Cartesian coordinate system.

Position in space is described using three mutually perpendicular axes $x$, $y$, $z$ meeting at an origin $O$; a point is then labelled by its coordinates $(x,y,z)$, the perpendicular distances from the three coordinate planes. Of the several ways to arrange three perpendicular axes, physics conventionally uses the right-handed system: curling the fingers of the right hand from the positive $x$-axis toward the positive $y$-axis makes the thumb point along positive $z$ — equivalently, viewed from the positive $z$-axis, the $x$-axis appears to rotate anticlockwise onto the $y$-axis. A left-handed system reverses this sense. The choice matters because formulas built from the vector cross product (torque, angular momentum, $\vec v=\vec\omega\times\vec r$) only come out with consistent, predictable signs if every calculation sticks to one convention — so physics fixes on right-handed throughout.