Justify,giving proper reasoning,whether the work done in the following case is positive or negative: Work done by an applied force on a body moving on a rough horizontal plane with uniform velocity.

$A$ person is climbing a palm tree:
$(i)$ What is the work done against the force of gravity?
$(ii)$ What is the work done by the force applied by the person if the person climbs $10 \, m$ and the mass of the person is $45 \, kg$?

State whether the following statement is true or false:
$A$ force does not work, if it produces no motion.

$(i)$ Define the term potential energy. Write the $SI$ unit of potential energy.
$(ii)$ $A$ body of mass $50 \, kg$ is situated at a height of $10 \, m$. What is its potential energy? (Given $g = 10 \, m s^{-2}$)

What is the work done by the tension in the string of a simple pendulum?

Four persons jointly lift a $250 \,kg$ box to a height of $1 \,m$ and hold it.
$(a)$ Calculate the work done by the persons in lifting the box.
$(b)$ How much work do they do just holding it?
$(c)$ Why do they get tired while holding it? $(g = 10 \,m/s^2)$