Question

Physics question A spacecraft descends vertically near the surface of Planet X. An upward thrust of 25.0kN from its engines slows it down at a rate of 1.20 m/s^2, but if an upward thrust of only 10.0 kN is applied, it speeds up at rate of .80m/s^2.

Answer 1

 F=m*a and m is constant on any planet 
25000-m*g=m*1.2 
10000-m*g=-m*0.80 
m*g is the weight 
25000/1.2-m*g/1.2=m 
10000/0.80-m*g/0.80=-25000/1.2+m*g/1.2 solve for m*g 
m*g=(10000/0.80+25000/1.2)/ (1/1.2+1/0.80) 
16 kN