**Question 1**

**Question 2**

In a perfectly ELASTIC collision between two perfectly rigid objects.

a) The momentum of each object is conserved.

b) The kinetic energy of each object is conserved.

c) The momentum of the system is conserved but the kinetic energy of the system is not conserved. d) Both the momentum and the kinetic energy of the system are conserved.

e) The kinetic energy of the system is conserved, but the momentum of the system is not conserved.

**Answer question 1**

**9. (A) momentum is always conserved, in elastic energy is also conserved.**

**10. (A)and(E)**

**since, angular velocity =w= constant**

**And, linear acceleration is given by,**

**a= w^2*R ……………(1)**

**and, linear velocity,**

**v= w*R ……………….(2)**

**11. (D)young modulus= (F/area)/(change in length/L)**

**let x m**

**so, 1*10^11= 100*1000/(x*10^-6)**

**so, x= 1m**

**Answer to question 2**

A *perfectly elastic collision*, or simply *elastic collision* is a collision ion which both the momentum as well as the kinetic energy of the objects remain constant in time.

On the other hand, if some of the kinetic energy of the colliding objects is lost during the collision, then the collision is called *inelastic collision*.

It must be noted that the total momentum of the colliding objects remain constant in all the cases.

Hence, the correct choice is **(d)**