2. Let's create a simple, two-period neoclassical model In this question, in period t you only use labor to make period output, and then you decide how much of that output to convert into capital that can be used later to help make period t+1 output. That means the "representative agent" has to decide how much of period t output to consume rather than save, but there's no such choice in period t+1. After all, t+1 is the end of time. Output is made in this very simple, constant returns to scale manner, so in each period double the input creates double the output: Y₁ = N₁ Y = 2K You get log utility from consumption in the first period, but square root in the second period Of course, you don't like work, so extra hours of work hurt your utility:

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2. Let's create a simple, two-period neoclassical model
In this question, in period t you only use labor to make period
t output, and then you decide how much of that output to convert into capital that
can be used later to help make period t+1 output. That means the "representative
agent" has to decide how much of period t output to consume rather than save, but
there's no such choice in period t+1. After all, t+1 is the end of time. Output is
made in this very simple, constant returns to scale manner, so in each period double
the input creates double the output:
Y₁ = N₁ Y zK
=
You get log utility from consumption in the first period, but square root in the second
period Of course, you don't like work, so extra hours of work hurt your utility:
U = ln(Ct) — mNt + 2(Ct+1)¹/²
In this simple economy with no externalities and perfect property rights, Adam
Smith's Invisible Hand Theorem will hold in its most optimistic form: A benevo-
lent social planner and a decentralized private market will yield exactly the same
answer. Since the "social planner problem" is simpler to solve mathematically than
the Smith-Hayek decentralized market outcome, we'll do what neoclassicals do so
often and we'll just solve the social planner problem.
Together, all of this means we can combine the utility function and the two produc-
tion functions to yield this utility function, which sums up all of the cruel tradeoffs:
U = ln(N − K) − mN + 2(zK)⁰.5
The two choice variables are N and K: everything else on the right hand side is an
exogenous fact of life from the social planner's point of view. Notice how N shows
up as both a good thing (part of current consumption) and a bad thing (work). Also
notice that K shows up as a bad thing (current saving, ugh sacrifice) and some-
thing good (it helps create future consumption). That's how you know you're doing
economics-tradeoffs are everywhere.
You're going to try to maximize well-being (U), so this is going to involve taking some
first derivatives and setting them equal to zero: That's the usual way to search for
a maximum.
1. F.O.C. of U with respect to N: 1/(N-K)
2. F.O.C. of U with respect to K: 1/(N-K) = (z/K)⁰.5
= m
QUESTIONS
1
Your first question to answer: What is the socially optimal level of K,
solely as a function of z and m? [I'd set the two F.O.C.s equal to each
other in order to eliminate the 1/(N-K), and then solve for K.]
2
Your second question is this: What is the socially optimal level of N,
solely as a function of z and m? [Once you know K solely as a function
of exogenous parameters z and m, it's probably easiest to find N by
plugging your solution for K into the first F.O.C.]
Your third question is this: If the marginal utility of leisure rises, what
happens to second-period consumption: Does it rise, fall, or remain un-
3 changed? [Leisure is the opposite of labor (N), so m is the marginal
utility of leisure. In calculus, this question
asking, What is the sign
of dC+1/dm ? It's just asking for a sign, you may be able to think it
through just based on the economics.
4
Your fourth question is this: If future productivity (z) rises, will current
labor supply rise as result, fall, or remain unchanged?
5
Your fifth question is this: In your answer to the fifth question, which is
winning out, the substitution effect (make hay while the sun shines) or
the income effect (you're gonna be rich someday, take it easy)?
Transcribed Image Text:2. Let's create a simple, two-period neoclassical model In this question, in period t you only use labor to make period t output, and then you decide how much of that output to convert into capital that can be used later to help make period t+1 output. That means the "representative agent" has to decide how much of period t output to consume rather than save, but there's no such choice in period t+1. After all, t+1 is the end of time. Output is made in this very simple, constant returns to scale manner, so in each period double the input creates double the output: Y₁ = N₁ Y zK = You get log utility from consumption in the first period, but square root in the second period Of course, you don't like work, so extra hours of work hurt your utility: U = ln(Ct) — mNt + 2(Ct+1)¹/² In this simple economy with no externalities and perfect property rights, Adam Smith's Invisible Hand Theorem will hold in its most optimistic form: A benevo- lent social planner and a decentralized private market will yield exactly the same answer. Since the "social planner problem" is simpler to solve mathematically than the Smith-Hayek decentralized market outcome, we'll do what neoclassicals do so often and we'll just solve the social planner problem. Together, all of this means we can combine the utility function and the two produc- tion functions to yield this utility function, which sums up all of the cruel tradeoffs: U = ln(N − K) − mN + 2(zK)⁰.5 The two choice variables are N and K: everything else on the right hand side is an exogenous fact of life from the social planner's point of view. Notice how N shows up as both a good thing (part of current consumption) and a bad thing (work). Also notice that K shows up as a bad thing (current saving, ugh sacrifice) and some- thing good (it helps create future consumption). That's how you know you're doing economics-tradeoffs are everywhere. You're going to try to maximize well-being (U), so this is going to involve taking some first derivatives and setting them equal to zero: That's the usual way to search for a maximum. 1. F.O.C. of U with respect to N: 1/(N-K) 2. F.O.C. of U with respect to K: 1/(N-K) = (z/K)⁰.5 = m QUESTIONS 1 Your first question to answer: What is the socially optimal level of K, solely as a function of z and m? [I'd set the two F.O.C.s equal to each other in order to eliminate the 1/(N-K), and then solve for K.] 2 Your second question is this: What is the socially optimal level of N, solely as a function of z and m? [Once you know K solely as a function of exogenous parameters z and m, it's probably easiest to find N by plugging your solution for K into the first F.O.C.] Your third question is this: If the marginal utility of leisure rises, what happens to second-period consumption: Does it rise, fall, or remain un- 3 changed? [Leisure is the opposite of labor (N), so m is the marginal utility of leisure. In calculus, this question asking, What is the sign of dC+1/dm ? It's just asking for a sign, you may be able to think it through just based on the economics. 4 Your fourth question is this: If future productivity (z) rises, will current labor supply rise as result, fall, or remain unchanged? 5 Your fifth question is this: In your answer to the fifth question, which is winning out, the substitution effect (make hay while the sun shines) or the income effect (you're gonna be rich someday, take it easy)?
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