There are many motivational methods used by managers. Let me list a few of them.
First, the most common method is the promise of a financial bonus. This is probably the most effective motivator, as people will work long hours and through difficult things, when they know that they could get a big bonus. The perfect example of this is the banking sector on Wall Street.
Second, the promise or hope of a promotion can also be a huge incentive. Often times there is also a raise in salary, but there may be other benefits as well. For example, there might be better hours, longer vacations, and so much more.
Third, manager might also use the idea of competition among other workers and departments to motivate people as well.