Define power. A boy of mass 45 kg climbs up 20 steps in 20 sec. it each step is 25 cm high, calculate the power of the boy used in climbing.

A man whose mass is 50 kg climbs up 30 steps of a stair in 30 s. If each step is 20 cm high, calculate the power used in climbing stairs.

A boy of mass 40 kg climbs vertically upwards on a coconut tree to a height of 10m. Calculate the work done by the boy.

A boy of mass 40 kg climbs vertically upwards on a coconut tree to a height of 10m. Calculate the potential energy gained.

A person carrying 10 bricks each of mass 2.5 kg. on his head moves to a height 20 metres in 50 seconds. Calculate the power spent in carrying bricks of the person.

A convex lens is made of glass of refractive index 1.5.If radius of curvature of the each of its twosurfaces is 20 cm,find the ratio of the power of the lens,when placed in air to its power ,when immersed inside a liquid of refractive index 1.25.

The focal length of th eye-piece and ojective a compound microscope are 5 cm and 1 cm respectively and the length of the tube is 20 cm.Calculate he magnifying power of the microscope,when the final image is formed at infinity .The value of least distance of ditinct vision is 25cm.

A compound microscope consists of an objective lens of focal length 2.0 cm and an eyepiece of focal length 6.25 cm separated by a distance of 15 cm. How far from the objective should an object be placed in order to obtain the final image at the least distance of distinct vision (25 cm)? What is the magnifying power of the microscope in?

A 10 kW drilling machine is used to drill a bore in a small aluminium block of mass 8.0 kg. How much is the rise in temperature of the block in 2.5 minutes, assuming 50% of power is used up in heating the machine itself or lost to the surroundings. Specific heat of aluminium = 0.91 J g^-1 ^@C^-1