$A$ 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?

$A$ girl of mass $35 \, kg$ sits on a trolley of mass $5 \, kg$. The trolley is given an initial velocity of $4 \, m \, s^{-1}$ by applying a force. The trolley comes to rest after covering a distance of $16 \, m$. $(a)$ What is the work done on the trolley? $(b)$ What is the work done by the girl?

$A$ car and a truck are moving with the same velocity of $60\, km h^{-1}$. Which one has more kinetic energy? (Mass of truck $ > $ Mass of car).

$A$ force of $10\, N$ moves a body with a constant speed of $2\, m s^{-1}$. Calculate the power of the body.

State whether the following statement is true or false:
When velocity is halved,its kinetic energy becomes $\frac{1}{4}^{th}$ of its original value.

Name at least three commonly used units of energy.