Water stored in a dam possesses

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

Calculate the amount of work done in moving a $50 \, kg$ mass through a distance of $10 \, m$ by applying a force of $100 \, N$. (in $, J$)

Two children $A$ and $B$ each weighing $20 \, kg$ climb a rope up to a height of $10 \, m$. Child $A$ takes $10 \, s$ and child $B$ takes $20 \, s$ to climb. State whether the work done by both is equal or unequal. Who has more power?

$(a)$ What is the commercial unit of energy? Give its relationship with the $SI$ unit of energy.
$(b)$ An electric bulb of $60 \,W$ is used for $10$ hours every day. How many units of electrical energy are consumed by this bulb in one day?

$(a)$ The potential energy of a freely falling object decreases progressively. Does this violate the law of conservation of energy? Why?
$(b)$ An object is dropped from a height $h$. When is its
$(i)$ potential energy maximum?
$(ii)$ kinetic energy maximum?