Not set Undergraduate

Dynamic of structures

Hello,
I need some help with the homework of dynamic of structures.
I send for you an example.
The homework starts Friday 6/19/2020 at 3.30 p.m. GMT+2 and it will take two hours, until 5.30 p.m. GMT +2. I put also correction of this example.
The homework will be similar.

Thanks in advance for your help..