An iron sphere of mass $30 \, kg$ has the same diameter as an aluminium sphere whose mass is $10.5 \, kg$. The spheres are dropped simultaneously from a cliff. When they are $10 \, m$ from the ground,they have the same:

$A$ porter moving vertically upstairs with a load on his head does work. Why?

An object of mass $1 \, kg$ has a potential energy of $1 \, J$ relative to the ground when it is at a height of: (in $, m$)

$A$ rocket is moving up with a velocity $v$. If the velocity of this rocket is suddenly tripled,what will be the ratio of the initial kinetic energy to the final kinetic energy?

Define kinetic energy and potential energy. Write an expression for $KE$ of a body of mass $m$ moving with speed $v$. Find the kinetic energy of a stone of $10 \, kg$ moving with a velocity of $10 \, m s^{-1}$.

Compare the power at which each of the following is moving upwards against the force of gravity? (given $g = 10 \, m \, s^{-2}$)
$(i)$ $A$ butterfly of mass $1.0 \, g$ that flies upward at a rate of $0.5 \, m \, s^{-1}$.
$(ii)$ $A$ $250 \, g$ squirrel climbing up on a tree at a rate of $0.5 \, m \, s^{-1}$.