Inertia is that property of a body by virtue of which the body is

State Newton's first law of motion.

Write answers to the following:
$(i)$ Mention the direction in which the force of friction acts on a moving body. State its units.
$(ii)$ Name the property of bodies (or objects) to resist a change in their state of rest or of motion. Name the quantity that is a measure of this property.
$(iii)$ Name the physical quantity whose unit is $kg\, m s^{-1}$. Define this quantity.

$A$ water tanker filled up to $2/3$ of its height is moving with a uniform speed. On sudden application of the brake,the water in the tank would

Why is it advised to tie luggage kept on the roof of a bus?

$A$ book of mass $2 \, kg$ is sliding with a constant velocity of $4 \, m s^{-1}$ on a frictionless horizontal table. What is the force required to keep the object moving with the same velocity (in $, N$)?