Define torque. Give its SI unit.

A uniform metre rule placed on a fulcrum at its middle point $O$ and having a weight $40 gf$ at $10 cm$ mark and a weight of $20 gf$ at the $90 cm$ mark, Is the metre rule in equilibrium? If not how will the rule turn?

Draw a diagram of a block and tackle system of pulleys having a V.R. of $5$. In your diagram, indicate clearly the points of application of load and effort.

A coin at the bottom of a trough containing water of refractive index $\frac{4}{3}$. The real depth of water is $14 \mathrm{cm}$. Find its apparent depth. Also, draw a ray diagram to explain it.

A ray of light is travelling from a medium $\mathrm{A}$ in which velocity of light is less into a medium where the velocity of light is more. Will it bend away or towards the normal?

A man standing in front of a vertical cliff fires a gun. He hears the echo after $3$ seconds. On moving closer to the cliff by $82.5 \mathrm{m}$, he fires again. This time, he hears the echo after $2.5$ seconds. Calculate the distance of the cliff from the initial position of man.

A man standing in front of a vertical cliff fires a gun. He hears the echo after $3$ seconds on moving closer to the cliff by $82.5 \mathrm{m}$, he fires again. This time, he hears the echo after $2.5$ seconds. Calculate the velocity of sound.