Circumference of a circle can be calculated if the radius or the diameter is given.
<u>Explanation</u>:
- Circumference or the perimeter of a circle can be calculated if the radius or the diameter of the circle is given.
- This is calculated by the formula -  2 * pi * r (if radius is given) and  pi * d (if diameter is given) where pi = 3.14, r = radius and d = diameter
- This calculation is based on the fact that the circumference is three and a little more times that of the radius. Since the diameter is double that of the radius, when the diameter is given formula becomes pi*d. 
 
        
             
        
        
        
Does this help at all to answer the question
 
        
             
        
        
        
The kinetic energy of the small ball before the collision is
                             KE  =  (1/2) (mass) (speed)²
                                     = (1/2) (2 kg) (1.5 m/s)
                                     =    (1 kg)  (2.25 m²/s²)
                                     =        2.25 joules.
Now is a good time to review the Law of Conservation of Energy:
                     Energy is never created or destroyed.  
                     If it seems that some energy disappeared, 
                     it actually had to go somewhere.
                     And if it seems like some energy magically appeared, 
                     it actually had to come from somewhere.
The small ball has 2.25 joules of kinetic energy before the collision.
If the small ball doesn't have a jet engine on it or a hamster inside,
and does not stop briefly to eat spinach, then there won't be any 
more kinetic energy than that after the collision.  The large ball 
and the small ball will just have to share the same 2.25 joules.
        
             
        
        
        
Answer:
Obviously the answer is Sun...