Define the term velocity.
Determine the rock's height above the planet's surface at time $t = 4.0\,\text{s}$.
A rock of mass $7.5\,\text{kg}$ is thrown vertically upwards from a planet's surface. It leaves the surface at a speed of $4.0\,\text{m s}^{-1}$ at time $t = 0$. The way the velocity $v$ of the rock varies with time $t$ is shown in Fig. 1.1. Assume that the planet has no atmosphere and that the viscous force on the rock is always zero.
Determine the change in momentum of the rock from $t = 0$ to $t = 4.0\,\text{s}$.
Determine the weight $W$ for the rock on this planet.
In reality, the planet in (b) has an atmosphere, so a viscous force acts on the moving rock. State and explain how, if at all, the resultant force on the rock varies as it moves vertically upwards.