Questions

Beats means the periodic increase and decrease in loudness heard when two notes of nearly the same frequency are sounded simultaneously.

Parabola, because when the coin is dropped at a particular point, it has the same velocity as the running train. So by Newton's first law, it continues its motion horizontally with that velocity. But then, it is also pulled down by earth's gravity continuously. In this situation its horizontal motion gives way to the parabolic motion until it reaches the ground.

Representative money is an item such as a token or piece of paper that has no intrinsic value but can be exchanged on demand for a commodity that does have intrinsic value, such as gold, silver, copper,...

Hence, a Check is an example of representative money.