This is based on momentum conservation method. You can find this problem in any textbooks. Also if you want to know the physical aspects about it search in youtube or see some websites available. See previous year neet or jee questions, you will found these type of problems were asked long ago. Hope it helps.

Valency is also called as the combining capacity of an element with other elements to form bonds. It is also ther number of vacant electrons left in the outer shell. They all have an outer shell with two electrons and are very reactive. Those elements in the second column have two electrons ready to make compounds. It shouldn't surprise you that calcium has a valence of 2.

Thankyou.

Hello,

Given that the shell is moving horizontally and explodes in two equal pieces. One particle is moving upward with a momentum 4p and the momentum at time of explosion is 3p.

Kinetic Energy = ?

By using law of conservation of momentum,

Total Momentum of particle before explosion = Total Momentum of particle after explosion

So, 3P ( i )= 4P ( j )  + P2

So, Magnitude of P2 = 5P

So, gain in Kinetic Energy

= ( 16 P^2 / m ) + ( 25 P^2 / m ) - ( 9 P^2 / 2m )

= 73 P^2 / 2m

Best Wishes.