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

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

$A$ spring which has been kept compressed by tying it is allowed to be dissolved in an acid. What happens to the potential energy of the spring?

What are the various energy transformations that occur when you are riding a bicycle?

Define work,energy,and power. Give the $SI$ units for each of these quantities. $A$ man whose mass is $80 \, kg$ climbs up $30$ steps of the stairs in $30 \, s$. If each step is $12.5 \, cm$ in height,calculate the power used in climbing the stairs. $(g = 10 \, m \, s^{-2})$

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