Q. 22

# The energy from the sun reaches just outside the earth’s atmosphere at a rate of 1400 W m^{–2}. The distance between the sun and the earth is 1.5 × 10^{11} m.

(a) Calculate the rate at which the sun is losing its mass.

(b) How long will the sun last assuming a constant decay at this rate? The present mass of the sun is 2 × 10^{30} kg.

Answer :

a)

The amount of energy radiated by the sun in

As the energy radiated is dependent on the surface area it covers which is given by

Energy loosed by the sun till it reaches earth in 1 second is given by

So, the mass loosed by the sun in 1 second is

b)

As the rate of decay of the mass is constant it will last up to

In years

Rate this question :

Find the speed at which the kinetic energy of a particle will differ by 1% from its nonrelativistic value 1/2 m_{0}v^{2}.

Through what potential difference should an electron be accelerated to give it a speed of

(a) 0.6c, (b) 0.9c and (c) 0.99 ?

HC Verma - Concepts of Physics Part 2

A 100W bulb together with its power supply is suspended from a sensitive balance. Find the change in the mass recorded after the bulb remains on for 1 year.

HC Verma - Concepts of Physics Part 2Find the increase in mass when 1 kg of water is heated from 0°C to 100°C. Specific heat capacity of water = 4200 J kg^{–1} K^{–1}.

Find the speed of an electron with kinetic energy

(a) 1 eV, (b) 10 keV and (c) 10 MeV.

HC Verma - Concepts of Physics Part 2

By what fraction does the mass of a spring change when it is compressed by 1 cm? The mass of the spring is 200g at its natural length and the spring constant is 500 N m^{–1}.

By what fraction does the mass of a boy increase when he starts running at a speed of 12 km h^{–1}?