[填空题]
At the surface of a g zxz2q9u/+qu1 /m.qgy1kto s + .8 zn6dfxxhh+tz0ujcertain planet, the gravitational acceleration g has a magnitude of 18f6h0xn d+jz xht .+uz2 m/s$^2$ A 21.0-kg brass ball is transported to this planet. What is (a) the mass of the brass ball on the Earth and on the planet
(b) the weight of the brass ball on the Earth and on the planet? $W_{Earth}$ $W_{planet}$
