Answer:
1. Under what condition(s) can an economy make a relatively quick and easy transition to full-employment level of output?
Classical economics are great theoretically, but actual evidence from real life is always against them. The problem with wages and unemployment is that wages are sticky, no one likes a wage cut and employees will always fight against them. That results in drastic changes in the level of unemployment, since it is easier to fire employees than lower their salaries.
When a demand shock occurs, and the aggregate demand curve shifts to the right, the aggregate supply curve will also shift. At this point, suppliers will need to hire more employees and fast since they cannot keep up with the demand. The problem is that in real life, demand shocks are sudden only in theory, no one will wake up tomorrow having twice the money and willing to spend it all immediately.
Classical economics work on the long run, but the problem is that the long run is not a definite point in time. We might actually never live to see the long run occur.
2. What condition(s) would keep an economy from moving back to full employment quickly and easily?
Shifts in the aggregate demand curve never occur from one day to another, they are gradual and take time. In real life, unless you suddenly win the lottery, the amount of goods that you purchase is generally stable. It will increase or decrease over time but not abruptly. Since sudden demand shocks do not occur in real life, neither do sudden shifts in the employment level. That is why the government issues monthly unemployment data, and you analyze the trends over several months or even years.