Can pilots play music in the cockpit?
Pilots may not have any distractions in the cockpit, and that includes music. Music is strictly prohibited in the cockpit unless there is a waiting period in which the plane is not in operation and no passengers are on board.
Is it important to applaud when the plane lands?
Although you might feel like celebrating at the end of a long flight, clapping upon landing is not necessary. You wouldn't applaud your bus driver for dropping you off at the correct destination—they're simply doing their job. Of course, if you feel like spreading some cheer, go for it.