Define watt. Express kilowatt in terms of joule per second. $A$ $150 \, kg$ car engine develops $500 \, W$ for each $kg$. What force does it exert in moving the car at a speed of $20 \, m \, s^{-1}$ (in $N$)?

State whether the following statement is true or false:
Kilowatt hour $(kWh)$ is the unit of power.

$(a)$ 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?

State whether the following statement is true or false:
When velocity is halved,its kinetic energy becomes $\frac{1}{4}^{th}$ of its original value.

$(a)$ State the law of conservation of energy.
$(b)$ Establish the relation between the $SI$ unit of energy and the commercial unit of energy.
$(c)$ $A$ toy car is displaced through $5 \, m$ on the application of a force of $7 \, N$. Assuming the force acts on the object throughout the displacement,what is the work done in this case?

$A$ girl is carrying a school bag of $3 \, kg$ mass on her back and moves $200 \, m$ on a levelled road. The work done against the gravitational force will be $(g = 10 \, m \, s^{-2})$.