To solve this problem we will apply Newton's second law, which indicates that the force is equivalent to the product between mass and acceleration, so
[tex]F = ma[/tex]
Here,
F= Force
m = Mass
a = Acceleration
Rearranging to find the mass we have,
[tex]m = \frac{F}{a}[/tex]
The value of the acceleration is
[tex]a = 18miles/hour^2 (\frac{0.00012417m/s^2}{1 miles/hour^2})[/tex]
[tex]a = 0.002235m/s^2[/tex]
Replacing to find the mass,
[tex]m = \frac{53kN}{0.002235m/s^2}[/tex]
[tex]m = \frac{53*10^{-3}}{0.002235}[/tex]
[tex]m = 23.71kg[/tex]
Now in ponds this value is
[tex]m = 23.71kg(\frac{2.205lb}{1kg})[/tex]
[tex]m=52.8 lb[/tex]
Therefore the mass of the spacecraft is 52.8lb