College Physics (7th Edition)

a). $147.5kJ$ b). $-122.5kJ$ c). $25kJ$
a). $h=\frac{1}{2}at^{2}=25m$ $F=m(g+a)=500(9.8+2)=5900N$ $W=5900\times25=147.5kJ$ b). $W=mgh=500\times(-9.8)\times25=-122.5kJ$ c). Net work done on helicopter $W=147.5-122.5=25kJ$