An object is placed 30 cm before a concave mirror of focal length of 20 cm to get a real
image. What will be the distance of the image from the mirror?

A certain house hold has consumed 320 units of energy during a month. How much energy is this in joules?

The radius of curvature of a concave mirror is 30 cm. Following Cartesian Sign Convention, its focal length is expressed as:

Which of the following statements is/are INCORRECT?
A. The value of G on the moon is equal to that on the earth.
B. $$26.68 \times 10^{-11} N$$ is the force of gravitation between two point masses of 2 kg and 2 kg kept 1 m apart.
C. Newton’s law of gravitation is valid in the laboratory only.
D. Force is inversely proportional to the square of the distance between two bodies.

Calculate the work done by the force of gravity when satellite moves in an orbit of
radius 40,000 km around the earth.