Final answer:
A drop in interest rates, increased federal spending on infrastructure, and firms becoming more optimistic about the economy and buying more capital goods all lead to an increase in aggregate demand in the short run.
Step-by-step explanation:
If interest rates have dropped for consumer loans, this will cause aggregate demand to increase in the short run. Lower interest rates lead to more affordable borrowing costs for both consumers purchasing big-ticket items such as houses and cars, and businesses investing in capital goods. As the cost of borrowing decreases, spending and investment typically rise, thus boosting aggregate demand.
Similarly, when the federal government pays for roads in Michigan to be fixed, this increases government spending, which shifts the aggregate demand curve to the right, resulting in aggregate demand increasing. This is due to more government spending on infrastructure leading to elevated business activities and services surrounding these projects.
Lastly, when firms become more optimistic about the economy and decide to buy more capital goods, they increase their investments, which also leads to an increase in aggregate demand in the short run. The optimism stimulates spending on business expansions and equipment, as firms anticipate a higher return on their investments due to the positive economic outlook.