Changes in the AD-AS Model - AP Macroeconomics

1. Based on the AD–AS model shown, the central bank raises the policy interest rate, reducing interest-sensitive spending and shifting aggregate demand in the short run. Which statement best compares the initial equilibrium $E_1$ with the new short-run equilibrium?
   Answer: The price level falls and real GDP falls. The AD-AS model shows how monetary policy affects the economy through interest rate channels that influence aggregate demand. When the central bank raises policy rates, borrowing becomes more expensive, reducing investment and interest-sensitive consumption, which shifts AD leftward from AD₁. The lower AD curve meets the unchanged SRAS curve below and to the left of E₁, so the new equilibrium has both a lower price level and lower real GDP. Students often forget that contractionary monetary policy affects both output and prices, not just one or the other. The key strategy is recognizing that higher interest rates shift AD left through reduced spending, then following the movement down along SRAS to find the new equilibrium with lower P and Y.
2. Based on the AD–AS model shown, the government raises personal income taxes, decreasing consumption and shifting aggregate demand in the short run. Starting from $E_1$, which combination of changes occurs at the new short-run equilibrium?
   Answer: The price level falls and real GDP falls. In the AD-AS framework, fiscal policy works through aggregate demand by affecting disposable income and spending. When government raises personal income taxes, households have less after-tax income, reducing consumption and shifting AD leftward from AD₁. The lower AD curve crosses the unchanged SRAS curve below and to the left of E₁, so the new equilibrium has both a lower price level and lower real GDP. Students sometimes think tax increases only reduce output, missing that decreased spending also eases price pressures. The key is recognizing that contractionary fiscal policy (higher taxes) shifts AD left, then following the movement down along SRAS to find the new equilibrium with lower P and Y.
3. Based on the AD–AS model shown, foreign incomes rise, increasing demand for the country's exports and shifting aggregate demand in the short run. Starting from $E_1$, which statement correctly identifies the short-run effect?
   Answer: The price level rises and real GDP rises. The AD-AS model shows how international trade affects domestic equilibrium through aggregate demand channels. When foreign incomes rise, overseas consumers demand more of our exports, increasing net exports (X-M) and shifting AD rightward from AD₁. The higher AD curve meets the unchanged SRAS curve up and to the right of E₁, so the new equilibrium has both a higher price level and higher real GDP. A common misconception is thinking export growth only boosts output, but increased foreign demand also creates inflationary pressure as the economy moves up along SRAS. The analytical strategy is to recognize that positive external demand shocks shift AD right, then trace the movement along SRAS to find the new equilibrium with higher P and Y.
4. Based on the AD–AS model shown, a productivity improvement lowers unit production costs, shifting short-run aggregate supply from $SRAS_1$ in the short run. Which outcome best describes the movement from $E_1$ to the new short-run equilibrium?
   Answer: The price level falls and real GDP rises from $E_1$ to the new equilibrium. In the AD-AS framework, productivity improvements affect the economy through the supply side by reducing production costs per unit of output. When productivity rises, firms can produce more at any given price level, shifting SRAS rightward from SRAS₁. The new short-run equilibrium lies where the unchanged AD curve crosses the shifted SRAS curve, down and to the right of E₁, resulting in a lower price level but higher real GDP—an ideal combination for economic growth. Students often confuse this with demand-driven growth, but productivity gains work through supply, allowing more output without inflationary pressure. To analyze supply-side improvements, identify that positive productivity shocks shift SRAS right, then follow the AD curve down to find the new equilibrium with lower P and higher Y.
5. Based on the AD–AS model shown, the government increases spending on infrastructure, which shifts aggregate demand in the short run. Which outcome best describes the change from the initial equilibrium $E_1$ to the new short-run equilibrium?
   Answer: The price level rises and real GDP rises from $E_1$ to the new equilibrium. Government purchases are a direct component of aggregate demand, so new infrastructure spending raises total spending at every price level. AD shifts rightward from AD₁ and crosses the unchanged SRAS curve at a new point. Moving up along the upward-sloping SRAS curve from E₁, the economy reaches a new short-run equilibrium with both a higher price level and higher real GDP. A common misconception is thinking that increased spending only affects output without impacting prices, but in reality, higher demand puts upward pressure on both. The key strategy is to identify which curve shifts (here, AD moves right) and then trace the movement along the stationary curve (SRAS) to find the new equilibrium with higher P and Y.
6. Based on the AD–AS model shown, a natural disaster disrupts supply chains and reduces productive capacity in the short run, shifting short-run aggregate supply. Which statement correctly classifies the change and identifies the short-run outcome?
   Answer: It is cost-push inflation, with a higher price level and lower real GDP at the new short-run equilibrium. The AD-AS model distinguishes between demand-pull inflation (from AD shifts) and cost-push inflation (from SRAS shifts). When natural disasters disrupt supply chains, production capacity falls and costs rise, shifting SRAS to the left. The new short-run equilibrium shows cost-push inflation: a higher price level combined with lower real GDP—the worst of both worlds economically. Students often confuse all inflation as demand-driven, but supply shocks create stagflation where prices rise despite falling output. The diagnostic strategy is to identify the source of the shift: if SRAS moves left due to higher costs or reduced capacity, expect cost-push inflation with the painful combination of higher P and lower Y.
7. Based on the AD–AS model shown, the central bank conducts an open-market purchase that increases the money supply, which shifts aggregate demand in the short run. Which statement correctly compares the initial equilibrium $E_1$ with the new short-run equilibrium?
   Answer: The price level rises and real GDP rises from $E_1$ to the new equilibrium. An open-market purchase works on the economy through aggregate demand: buying bonds adds bank reserves, expands the money supply, and pushes interest rates down, which stimulates investment and interest-sensitive consumption. That extra spending shifts AD rightward from AD₁. The shifted AD curve crosses the unchanged SRAS curve above and to the right of E₁, so the new short-run equilibrium has both a higher price level and higher real GDP. A common error is thinking monetary expansion only boosts output, but increased spending also bids up prices as the economy moves along the upward-sloping SRAS. To analyze monetary policy effects, first identify that expansionary policy shifts AD right, then trace the movement up along SRAS to find the new equilibrium with higher P and Y.
8. Based on the AD–AS model shown, consumer confidence falls sharply, reducing consumption and shifting aggregate demand in the short run. What is the short-run change in the price level and real GDP as the economy moves from $E_1$ to the new short-run equilibrium?
   Answer: The price level falls and real GDP falls. The AD-AS model illustrates how changes in spending behavior affect macroeconomic equilibrium through shifts in aggregate demand. When consumer confidence falls sharply, households reduce consumption spending, causing AD to shift leftward from AD₁. With SRAS unchanged, the shifted AD curve crosses SRAS down and to the left of E₁, so the new short-run equilibrium has both a lower price level and lower real GDP. Many students incorrectly assume that reduced demand only lowers output, forgetting that decreased spending also reduces pressure on prices. The key insight is that leftward AD shifts create recessionary conditions with both P and Y falling as the economy slides down along the SRAS curve to the new equilibrium.
9. Based on the AD–AS model shown, a sudden increase in oil prices raises firms' production costs, shifting short-run aggregate supply in the short run. Compared with the initial equilibrium $E_1$, what happens to the price level and real GDP at the new short-run equilibrium?
   Answer: The price level rises and real GDP falls. An oil price spike is a classic negative supply shock: energy is an input to almost everything, so firms' production costs rise and the short-run aggregate supply (SRAS) curve shifts leftward from SRAS₁. With AD unchanged, the new SRAS crosses AD at a higher price level but lower real GDP than at E₁—this combination is called stagflation. Students often mistakenly think supply shocks only affect prices, but remember that leftward SRAS shifts reduce the economy's ability to produce at any given price level. The strategy is to recognize cost shocks shift SRAS left, then follow the AD curve to find where higher prices coincide with lower output.
10. Based on the AD–AS model shown, firms cut back on planned investment spending due to pessimistic profit expectations, which shifts aggregate demand in the short run. Compared with $E_1$, which outcome occurs at the new short-run equilibrium?
    Answer: The price level falls and real GDP falls from $E_1$ to the new equilibrium. Investment is the most volatile component of aggregate demand because it rests on firms' expectations about future profits. When firms turn pessimistic and cut planned investment, total spending falls at every price level, shifting AD leftward from AD₁. The shifted AD curve meets the unchanged SRAS curve below and to the left of E₁, so the new short-run equilibrium has both a lower price level and lower real GDP. A common error is thinking reduced investment only affects output, but decreased spending also reduces inflationary pressure. The analytical approach is to recognize that negative investment shocks shift AD left, then trace the movement down along SRAS to find the recessionary equilibrium with lower P and Y.

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