$A$ body of mass $5\, kg$ initially at rest is subjected to a force of $20\, N$. Find the kinetic energy acquired by the body at the end of $10\, s$. (in $, J$)

$(a)$ 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?

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:

$A$ box of mass $10 \, kg$ is placed at point $A$ on a horizontal surface. It is moved to point $B$,which is at a distance of $2 \, m$ from $A$. If the line joining $A$ and $B$ is horizontal,find the work done by the gravitational force on the box. Justify your answer. $(g = 10 \, m s^{-2})$ (in $, J$)

Define work,energy,and power. Give the $SI$ units for each of these quantities. $A$ man whose mass is $80 \, kg$ climbs up $30$ steps of the stairs in $30 \, s$. If each step is $12.5 \, cm$ in height,calculate the power used in climbing the stairs. $(g = 10 \, m \, s^{-2})$

Write the relation between the commercial unit of electricity and the $SI$ unit of energy.