What were the economic motivations for the u. s. to complete the panama canal?

 Before the Panama Canal was built all shipping (military, trade, passenger, etc) had to travel all the way around South America to reach the either the east or west coast. The Panama Canal cut the trip down by thousands of miles. During the time period the U.S. navy was becoming a major world force and the president at the time (Theodore Roosevelt) was determined to created a canal that would massively increase the efficiency of the navy.

It was to have a quicker passage from the Pacific to the Atlantic and vice versa

Yes, some people used the depression to the max. not everybody had stocks, and those that didn't bought many things inexpensive, so that when prices rose again, they were much more richer than beforehope this