How many watts are there in $1$ horsepower (in $watts$)?

When a ball is thrown vertically upwards,its velocity goes on decreasing. What happens to its potential energy as its velocity becomes zero?

$(a)$ Define power. Give its $SI$ unit.
$(b)$ Taking the example of a simple pendulum, explain the variations in the forms of energy and the interconversions involved.

$A$ $2 \, m$ high person is holding a $25 \, kg$ trunk on his head and is standing at a roadways bus-terminus. How much work is done by the person (in $, J$)?

In case of negative work,the angle between the force and displacement is: (in $^o$)

$(a)$ What is meant by potential energy? Is potential energy a vector or scalar quantity?
$(b)$ Give one example of a body having potential energy.