Need help with these two physics problemsProblem $4$: Train Spring

Some train stations have large horizontal springs at the ends of the tracks. These are safety devices to stop the train so that it will not go plowing through the station in the event an engineer is too busy texting. You would like to know how fast a train could be going and still be safely stopped by the spring. It looks like the maximum compression of the spring is about $3\mathrm{.}0$ meters. The maximum safe acceleration for passengers while stopping is about half of g $.$

Hint: You will need to use both conservations of energy and Newton's second law.

Problem $5$: Airplane Launcher

You are a Navy officer ordered to design an effective airplane launcher. The launcher consists of a large spring that pushes the plane for the first $6$ meters of a $22$ meter long runway. The plane's engines can supply a constant thrust of $5\mathrm{.}4$E$4$N for the entire length of the runway. In order for the two $($metric$)$ ton plane to successfully take off, it must have a speed of at least $44\frac{m}{s}$ by the end of the runway.

What is the minimum spring constant for the launcher?

Using this spring, what will be the maximum acceleration of the plane $($and its pilot$)?$

Based on this maximum acceleration, do you think this is a good design for the safety of the pilots? Why or why not?

If you desired to decrease the maximum acceleration, then what would you suggest changing $($thrust$,$ mass, spring, runway, etc.$)?$ Be specific and provide numbers. Assume you cannot change the needed speed.