The calories of heat developed in 200 W heater in 7 min is estimated

Options

A. 15000
B. 100
C. 1000
D. 20000

Explanation

To solve the problem of estimating the calories of heat developed in a 200 W heater in 7 minutes, we can follow these steps:

### Step 1: Identify the given values
- Power (P) = 200 W (watts)
- Time (T) = 7 minutes

### Step 2: Convert time from minutes to seconds
Since power is given in watts (joules per second), we need to convert the time from minutes to seconds:
\[ T = 7 \text{ minutes} \times 60 \text{ seconds/minute} = 420 \text{ seconds} \]

### Step 3: Calculate the heat developed in joules
Using the formula for heat developed (H):
\[ H = P \times T \]
Substituting the values:
\[ H = 200 \text{ W} \times 420 \text{ seconds} \]
\[ H = 84000 \text{ joules} \]

### Step 4: Convert joules to calories
We know that 1 calorie = 4.2 joules. To convert joules to calories, we use the conversion factor:
\[ \text{Calories} = \frac{\text{Joules}}{4.2} \]
Substituting the value of heat in joules:
\[ \text{Calories} = \frac{84000 \text{ joules}}{4.2} \]
Calculating this gives:
\[ \text{Calories} \approx 20000 \text{ calories} \]

### Final Answer
The heat developed in the 200 W heater in 7 minutes is approximately **20,000 calories**.

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