If an electric iron of $1200 \, W$ is used for $30$ minutes everyday, find the electric energy consumed in the month of April. (in $kWh$)

$(a)$ Define one watt.
$(b)$ $A$ lamp consumes $1000 \ J$ of electrical energy in $10 \ s$. What is its power?

$A$ $1 \, kg$ mass has a kinetic energy of $1 \, J$ when its speed is: (in $, m/s$)

$(i)$ Derive an expression for the kinetic energy of an object. Write the $SI$ unit of kinetic energy.
$(ii)$ An object of mass $10 \, kg$ is moving with a uniform velocity of $5 \, m s^{-1}$. Calculate the kinetic energy possessed by the object.

Four men lift a $250 \,kg$ box to a height of $1 \,m$ and hold it without raising or lowering it. $(a)$ How much work is done by the men in lifting the box? $(b)$ How much work do they do in just holding it? $(c)$ Why do they get tired while holding it? $(g = 10 \,m \,s^{-2})$

The velocity of a body moving in a straight line is increased by applying a constant force $F$ for some distance in the direction of the motion. Prove that the increase in the kinetic energy of the body is equal to the work done by the force on the body.