I think it's 3. within an outer arm
Not only in converting temperatures I think, we always use significant figures every time we want to make some experimental report using the exact data from our experiment. If that isn't experimental report ( some exercise/questions from your textbook) it's not necessary
there are a reading of something like s-waves and p-waves they tell if an earthquakes coming.
Answer with Explanation:
We are given that
Mass of superman=m=78 kg
Mass of train=m'=17863 kg
Speed of train=u'=75 km/h=

Let initial speed of superman=u
Momentum=mv
Using the formula



Average horizontal force=0.58
Deceleration 
Final speed of train=v'=0

Using the formula





Using the formula


