The atomic mass unit is the atomic number of an element plus the number of neutrons in an element. Elements such as carbon, copper and lithium on the periodic table. Atomic Mass = Atomic number + Number of Neutrons.
Answer:
Explanation:
Given
mass of lumber jack 
mass of floating log 
velocity of lumber jack =3.74 m/s (w.r.t. shore)
conserving momentum
Initial momentum=Final momentum



(b)For second Log
Conserving Momentum
Initial momentum of log and Lumber jack=Final momentum of log and lumberjack

u is final velocity of lumberjack and log


He had their masses and reactivity. I hope this helps.