Part (a)
The time taken by the shell to strike on the ground can be given as,
[tex]t=\frac{2u\sin \theta}{g}[/tex]
Plug in the known values,
[tex]\begin{gathered} t=\frac{2(500\text{ m/s)sin53}}{10m/s^2} \\ =(100\text{ s)(}0.799) \\ \approx80\text{ s} \end{gathered}[/tex]
Therefore, the time after which the shell strikes on the ground is 80 s.
Part (b)
The horizontal distance covered by the shell is,
[tex]d=u_xt[/tex]
The horizontal speed of the shell is,
[tex]u_x=u\cos \theta[/tex]
Therefore, the distance covered becomes,
[tex]d=(u\cos \theta)t[/tex]
Substituting values,
[tex]\begin{gathered} d=(500\text{ m/s)cos53(80 s)} \\ =(40000\text{ m)(}0.602) \\ =24080\text{ m} \end{gathered}[/tex]
Therefore, the horizontal distance covered by the shell is 24080 m.