3) a stretched rubber band
No it would not be static friction.
Here since both children and merry go round is our system and there is no torque acting on this system
So we will use angular momentum conservation in this

now here we have



Now when children come to the position of half radius
then we will have



now from above equation we have


To answer this question, we will refer to the attached diagram which represents the complete rock cycle.
Rock 1:Formed when rock 2 and rock 3 were subjected to intense heat and pressure inside the earth.
Referring to the diagram, we will find that heat and pressure are the factors required to form metamorphic rocks
Therefore, rock 1 is metamorphicRock 2:Formed when rock 1 and rock 3 were broken down into mineral (sediments) which accumulate and are subjected to pressure.
Referring to the diagram, we will find that this description would lead to the formation of sedimentary rocks.
Therefore, rock 2 is a sedimentary rock.Rock 3:Formed when rock 1 and rock 2 were buried inside the earth and melted because of heat and magma.
Referring to the diagram, we would find that melting then cooling of magma would lead to formation of igneous rock.
Therefore, rock 3 is igneous rock.Based on the above, the correct choice would be:Rock 1: Metamorphic
Rock 2: Sedimentary
Rock 3: Igneous