Question 832 of 949
A car travels 150 kilometers north in 2 hours and then 50 kilometers south in 1 hour. What is the average velocity of the car for the entire journey?
- 50 km/h north
- 66.67 km/h north
- 100 km/h north
- 100 km/h south
Correct Answer:
B
Explanation
To find the average velocity of the car for the entire journey, we need to follow a systematic approach. Let's break it down step-by-step.
### Step 1: Understand the Journey
The car travels in two segments:
1. **First Segment**: 150 kilometers north in 2 hours.
2. **Second Segment**: 50 kilometers south in 1 hour.
### Step 2: Calculate Total Displacement
Displacement is the overall change in position from the starting point to the final position, taking direction into account.
- **Displacement from the first segment**: 150 km north.
- **Displacement from the second segment**: 50 km south.
To find the total displacement, we can treat north as positive and south as negative:
- Total Displacement = Displacement from the first segment - Displacement from the second segment
- Total Displacement = 150 km (north) - 50 km (south) = 150 km - 50 km = 100 km north.
### Step 3: Calculate Total Time
Next, we need to calculate the total time taken for the journey:
- Time for the first segment = 2 hours.
- Time for the second segment = 1 hour.
Total Time = Time for the first segment + Time for the second segment
Total Time = 2 hours + 1 hour = 3 hours.
### Step 4: Calculate Average Velocity
Average velocity is defined as the total displacement divided by the total time taken. The formula for average velocity (\(v_{avg}\)) is:
\[
v_{avg} = \frac{\text{Total Displacement}}{\text{Total Time}}
\]
Substituting the values we calculated:
\[
v_{avg} = \frac{100 \text{ km (north)}}{3 \text{ hours}} \approx 33.33 \text{ km/h (north)}
\]
### Step 5: Analyze the Options
Now, let's look at the options provided:
- A. 50 km/h north
- B. 66.67 km/h north
- C. 100 km/h north
- D. 100 km/h south
### Step 6: Evaluate Each Option
- **Option A (50 km/h north)**: This is incorrect because the average velocity calculated is approximately 33.33 km/h, not 50 km/h.
- **Option B (66.67 km/h north)**: This is incorrect as well; our calculation shows the average velocity is approximately 33.33 km/h, not 66.67 km/h.
- **Option C (100 km/h north)**: This is also incorrect; the average velocity is not 100 km/h.
- **Option D (100 km/h south)**: This is incorrect because the average velocity is positive (north), and the magnitude is not 100 km/h.
### Conclusion
None of the options provided match the calculated average velocity of approximately 33.33 km/h north. Therefore, it seems there may have been an error in the options given or the expected answer.
### Revision Summary
- Average velocity is calculated using total displacement divided by total time.
- Displacement considers direction; north is positive, and south is negative.
- The total displacement for the journey was 100 km north, and the total time was 3 hours.
- The average velocity calculated was approximately 33.33 km/h north, which does not match any of the provided options.
Make sure to double-check the options in your exam, as they may contain errors or misinterpretations.