( ( a -RRB- ) ( ( ( ( ( ( ( The ( net force ) ) ( on ( the ( elevator car ) ) ) ) ( points up ) ) , ) since ) ( ( the car ) ( is ( moving upward ) ) ) ) . ) )
(ROOT (S (LST (LS a) (-RRB- -RRB-)) (S (NP (NP (DT The) (JJ net) (NN force)) (PP (IN on) (NP (DT the) (NN elevator) (NN car)))) (VP (VBZ points) (PRT (RP up)))) (, ,) (ADVP (RB since)) (S (NP (DT the) (NN car)) (VP (VBZ is) (VP (VBG moving) (ADVP (RB upward))))) (. .)))
a) The net force on the elevator car points up, since the car is moving upward.
(ROOT (S (NP (DT A) (VBG moving) (NN car)) (VP (VBZ is) (VP (VBN said) (S (VP (TO to) (VP (VB be) (PP (IN in) (NP (JJ dynamic) (NN equilibrium))) (SBAR (WHADVP (WRB when)) (S (NP (PRP it)) (VP (VBZ is) (NP (CD zero) (JJ net) (NN force)))))))))) (. .)))