$A$ spring which has been kept compressed by tying its ends together 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?

$(a)$ Define average power. Calculate the total energy consumed in the month of November in a household in which four devices of power $500\, W$ each are used daily for $10\, hours.$
$(b)$ $A$ freely falling object eventually stops on reaching the ground. What happens to its energy?

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

What is the work done by the force of gravity in the following cases?
$(a)$ $A$ satellite moving around the Earth in a circular orbit of radius $35000 \, km$.
$(b)$ $A$ stone of mass $250 \, g$ is thrown up to a height of $2.5 \, m$.

$(a)$ 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.