A model hovercraft travelling north has a mass of 800 g. Its fan produces a force of 0.60 N northwards, while a force of 2.2 N acts southwards. What is its acceleration?
2.0 m s−22.0\ \mathrm{m\,s^{-2}}2.0 ms−2 southwards
0.75 m s−20.75\ \mathrm{m\,s^{-2}}0.75 ms−2 northwards
0.0020 m s−20.0020\ \mathrm{m\,s^{-2}}0.0020 ms−2 southwards
3.5 m s−23.5\ \mathrm{m\,s^{-2}}3.5 ms−2 southwards