A radio isotope X with a half life 1.4 x 10⁹ yr decays of Y which is stable. A sample of the rock from a cave was found to contain X and Y in the ratio 1:7. The age of the rock is,

• 1.96 x 10⁹ yr

• 3.92 x 10⁹ yr

• 4.20 x 10⁹ yr

• 4.20 x 10⁹ yr

The half-life of radioactive isotope X is 20 yr. It decays to another element Y which is stable.The two elements X and Y were found to be in the ratio 1:& in a sample of given rock is estimated to be

• 40 yr

• 60 yr

• 80 yr

• 80 yr

A radioactive nucleus of mass M emits a photon of frequency v and the nucleus recoils.The recoil energy will be

• h²v² / 2Mc²

• zero

• hv

• hv

The power obtained in a reactor using U²³⁵ disintegration is  1000kW. The mass decay of U²³⁵ per hour is

• 20 μg

• 40 μg

• 1 μg

• 1 μg

The half - life of a radioactive isotope X is 50 yr. It decays to another element Y which is stable. The two elements X and Y were found to be in the ratio of 1: 15 in a sample of a given rock. The age of the rock was estimated to be

• 200 yr

• 250 yr

• 100 yr

• 100 yr

Fusion reaction takes place at high temperature because

• atoms get ionised at high temperature

• kinetic energy is high enough to overcome the coulomb repulsion between nuclei

• molecules break up at high temperature

• molecules break up at high temperature

A nucleus  emits one α - particle and two β^- particles. The resulting nucleus is 

138.

A nucleus of uranium decays at rest into nuclei of thorium and helium. Then, 

• the helium nucleus has more kinetic energy than the thorium nucleus

• the helium nucleus has less momentum than the thorium nucleus

• the helium nucleus has more momentum than the thorium nucleus

• the helium nucleus has more momentum than the thorium nucleus

Two radioactive nuclei P and Q, in a given sample decay into a stable nucleous R. At time t =0, number of P species are 4N_o and that of Q are N_o.Half -life of P (for conversion to R) is 1 min where asthat of Q is 12 min. Initially there are no nuclei of R present in the sample. When number of nuclei of R presnent in the sample would be

• 3N_o

• 9N_o / 2

• 5N_o/2

• 5N_o/2

The mass of a  nucleus is 0.042u less than the sum of the masses of all its nucleons. The binding energy per nucleon is  nucleus is nearly

• 46 MeV

• 5.6 MeV

• 3.9 MeV

• 3.9 MeV