Let's analyze the problem step-by-step. --- ## Part (c): Graphically depict the output, price, and profit of a monopolistically competitive firm in the short run ### Step 1: Understand the given data - The firm faces a **U-shaped average cost curve (AC)** with a **constant marginal cost (MC)**, say \( c \). - The **market demand curve** is downward sloping, with a **market price \( P \)** that is **above the minimum of the AC curve**. - The firm operates in the **short run**. ### Step 2: Basic assumptions - Since \( c \) is constant, the **MC** curve is a horizontal line at \( c \). - **Price \( P \)** is above the **minimum average cost**, so the firm makes **supernormal profit** in the short run. ### Step 3: Graphical depiction - Draw the **U-shaped average cost curve (AC)**. - Draw the **marginal cost (MC)** curve as a horizontal line at \( c \). - Draw the **market demand curve \( D \)**, which is downward sloping. - Find the **profit-maximizing output \( Q^* \)** where **MC = MR** (marginal revenue). For simplicity, assume the firm sets \( Q^* \) where \( MC = MR \), and the corresponding **price \( P^* \)** on the demand curve at \( Q^* \). - The **average revenue (AR)** curve coincides with the demand curve \( P \). ### Step 4: Determine profit area - The **profit per unit** is \( P^* - AC(Q^*) \). - The **total profit** is represented as the **rectangle** with height \( P^* - AC(Q^*) \) and width \( Q^* \). --- ## Part (d): Describe the process whereby supernormal profits are eroded and ultimately disappear in the long run ### Step 1: Recognize the impact of supernormal profits - When firms in a monopolistically competitive market earn **supernormal profits**, **new firms** are attracted to the market due to the **profit incentive**. ### Step 2: Entry of new firms - The entry of new firms increases **product differentiation** options and **market supply**, causing the **market demand curve** faced by existing firms to **shift inward** (or the individual firm's demand curve to **become more elastic**). ### Step 3: Shift in demand curve - As **more firms** enter, the **demand curve** for each existing firm **shifts leftward** (becomes flatter) because consumers now have more substitutes. ### Step 4: Adjustment of equilibrium - The **price** that the firm can charge **decreases**. - The **supernormal profit** diminishes as the **price approaches the average cost**. - Eventually, the **price equals the average cost** at the profit-maximizing output. ### Step 5: Long-run equilibrium - **Supernormal profits** are **eroded**. - The firm makes **normal profit** (zero economic profit). - **Entry stops** because no more supernormal profits attract new firms. --- ## **Summary:** - **Graphically (short run):** The firm operates where \( MC = MR \), with the price on the demand curve above the AC curve, resulting in supernormal profits. - **Long run:** Entry of new firms shifts the demand curve inward, reducing the firm's price and supernormal profits until only normal profit remains. --- **Final notes:** This process illustrates classic monopolistic competition dynamics where **free entry and exit** lead to **normal profits** in the long run. --- Let me know if you'd like me to create a detailed diagram or further elaboration!

The average cost curve (AC) is U-shaped, indicating initial economies of scale, while the constant marginal cost (MC) line remains horizontal. This implies that production costs per unit stabilize after a certain output level.