Write Aristotle’s law regarding motion.

Define $SI$ unit of force $N$. Define $CGS$ unit of force dyne.

For a free body diagram shown in the figure, the four forces are applied in the ' $x$ ' and ' $y$ ' directions. What additional force must be applied and at what angle with positive $x$-axis so that the net acceleration of body is zero?

A mass of $5\, kg$ is suspended by a rope of length $2\,m$ from a ceiling. A force of $50\,N$ in the horizontal direction is applied at the mid-point of the rope. The angle made by the rope with the vertical, in equilibrium is ........ $^o$

An object of mass $5\, kg$ is thrown vertically upwards from the ground. The air resistance produces a constant retarding force of $10\, N$ throughout the motion. The ratio of time of ascent to the time of descent will be equal to $\left[\right.$Use $g =10 \,ms ^{-2}]$

There are three forces $\vec {F_1}$, $\vec {F_2}$ and $\vec {F_3}$ acting on a body, all acting on a point $P$ on the body. The body is found to move with uniform speed.

$(a)$ Show that the forces are coplanar.

$(b)$ Show that the torque acting on the body about any point due to these three forces is zero.