Step-by-step explanation:
Using the law of the conservation of linear momentum P:
P_i = P_fP 
i
 =P 
f
 
so:
M_mV_{mi}+M_pV_{pi} = M_sV_sM 
m
 V 
mi
 +M 
p
 V 
pi
 =M 
s
 V 
s
 
where M_mM 
m
 is the mass of the man, V_{mi}V 
mi
 is the initial velocity of the man, M_pM 
p
 is the mass of the puck, V_{pi}V 
pi
 is the initial velocity of the puck, M_sM 
s
 is the mass of the puck and the man and V_sV 
s
 is the velocity of both after the collition.
Replacing values, we get:
(80kg)(0m/s)+(0.17kg)(20m/s) = (80kg + 0.17kg)V_s(80kg)(0m/s)+(0.17kg)(20m/s)=(80kg+0.17kg)V 
s
 
Finally, solving for V_sV 
s
 :
V_sV 
s
 =0.0424m/s