An object of mass $40 \text{ kg}$ is pulled up to a height of $0.5 \text{ m}$. Calculate the work done. (Given $g = 9.8 \text{ m s}^{-2}$) (in $J$)

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:

State the type of energy transformation in the following cases: $(a)$ in a loudspeaker $(b)$ solar battery.

What is the work done by the force of gravity in the following cases?
$(a)$ $A$ satellite moving around the Earth in a circular orbit of radius $35000 \, km$.
$(b)$ $A$ stone of mass $250 \, g$ is thrown up to a height of $2.5 \, m$.

Four persons jointly lift a $250 \,kg$ box to a height of $1 \,m$ and hold it.
$(a)$ Calculate the work done by the persons in lifting the box.
$(b)$ How much work do they do just holding it?
$(c)$ Why do they get tired while holding it? $(g = 10 \,m/s^2)$

$A$ block of mass $5 \,kg$ is lying on a frictionless table. $A$ force of $20 \,N$ is applied on it for $10 \,s$. Calculate its kinetic energy. (in $J$)