Because you need to have a guess to know what to argue or explain in your experiment
Answer:
Impulse will be 12 kgm/sec
So option (b) will be correct option
Explanation:
We have given mass of the baseball m = 0.15 kg
Ball speed before hit 
Ball speed after hitting
( negative direction due to opposite direction )
We have to find the impulse
We know that impulse is equal; to the change in momentum
So change in momentum = 
So option (b) will be correct option
Answer:
To determine how efficient that system is.
The particles vibrate against each other in a soild state........i think