Policeman with energy to get through (4)
I believe the answer is:
cope
'to get through' is the definition.
(to get through something is to cope with it)
'policeman with energy' is the wordplay.
'policeman' becomes 'cop' (slang term).
'with' means one lot of letters go next to another.
'energy' becomes 'e' (physics symbol as in E=mc2).
'cop'+'e'='COPE'
(Other definitions for cope that I've seen before include "Priest's cloak; deal (with)" , "Deal with, manage successfully" , "top on wall" , "special cloak" , "Deal effectively (with a difficulty)" .)