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? $(g = 10 \,m \,s^{-2})$

Define: $(a)$ power $(b)$ work done $(c)$ kinetic energy. Give the $SI$ unit of each.

What would be the amount of work done on an object by a force,if the displacement of the object is zero?

Justify,giving proper reasoning,whether the work done in the following case is positive or negative: Work done by friction on a body sliding down an inclined plane.

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

$(a)$ The Earth,moving around the Sun in a circular orbit,is acted upon by a force,and hence work must be done on the Earth by the force. State whether the statement is correct or not. Give reasons for your answer.
$(b)$ $A$ coolie holding a heavy box is waiting at the bus stand for $15$ minutes. How much work is done by him?
$(c)$ $A$ man weighing $70 \, kg$ carries a weight of $10 \, kg$ to the top of a tower $100 \, m$ high. Calculate the work done by the man. $(g = 10 \, m s^{-2})$