A seismometer on the surface of a planet has a mass of 8.0 kg and a weight of 20 N. What is the gravitational field strength at the surface of the planet?
12 N kg−112\ \mathrm{N\,kg^{-1}}12 Nkg−1
2.5 N kg−12.5\ \mathrm{N\,kg^{-1}}2.5 Nkg−1
0.40 N kg−10.40\ \mathrm{N\,kg^{-1}}0.40 Nkg−1
160 N kg−1160\ \mathrm{N\,kg^{-1}}160 Nkg−1