Given
The velocity of the carriage, v=18 m/s
The kinetic energy is , K=90 J
To find
The mass of the carriage
Explanation
Let the mass of the carriage be m
Thus,
[tex]\begin{gathered} K=\frac{1}{2}mv^2=90 \\ \Rightarrow\frac{1}{2}m\times18^2=90 \\ \Rightarrow m=0.55\text{ kg} \end{gathered}[/tex]Conclusion
The mass is 0.55kg