Question 69 of 480
A predator moves in a circle of radius √2 centre (0,0), while a prey moves along the line y = x. If 0 \(\leq\) x \(\leq\) 2, at which point(s) will they meet?
- A. (1,1) only
- B. (1,1) and (1,2)
- C. (0,0) and (1,1)
- D. (√2,√2) only
Correct Answer:
A
Explanation
To determine the points at which the predator and prey meet, we need to analyze their respective paths mathematically.
### Step 1: Define the paths of the predator and prey
1. **Predator's Path**: The predator moves in a circle with a radius of \(\sqrt{2}\) centered at the origin (0,0). The equation of a circle is given by:
\[
x^2 + y^2 = r^2
\]
For our predator, substituting \(r = \sqrt{2}\):
\[
x^2 + y^2 = (\sqrt{2})^2 = 2
\]
2. **Prey's Path**: The prey moves along the line defined by the equation \(y = x\). This means for any point on this line, the y-coordinate is equal to the x-coordinate.
### Step 2: Substitute the prey's path into the predator's equation
To find the points of intersection, we substitute \(y = x\) into the predator's equation:
\[
x^2 + (x)^2 = 2
\]
This simplifies to:
\[
2x^2 = 2
\]
Dividing both sides by 2 gives:
\[
x^2 = 1
\]
Taking the square root of both sides, we find:
\[
x = 1 \quad \text{or} \quad x = -1
\]
### Step 3: Find corresponding y-coordinates
Since \(y = x\), we can find the corresponding y-coordinates:
- If \(x = 1\), then \(y = 1\). Thus, one point of intersection is \((1, 1)\).
- If \(x = -1\), then \(y = -1\). Thus, another point of intersection is \((-1, -1)\).
### Step 4: Check the range of the prey's movement
The problem states that the prey moves along the line \(y = x\) for \(0 \leq x \leq 2\). This means we only consider points where \(x\) is non-negative. Therefore, the point \((-1, -1)\) is not valid since it falls outside the specified range.
### Step 5: Valid points of intersection
The only valid point of intersection within the specified range is:
\[
(1, 1)
\]
### Step 6: Evaluate the options
Now, let's evaluate the provided options:
- **A. (1,1) only**: This is correct as it is the only valid intersection point.
- **B. (1,1) and (1,2)**: Incorrect. While (1,1) is valid, (1,2) does not satisfy the predator's circular path.
- **C. (0,0) and (1,1)**: Incorrect. (0,0) is not on the line \(y = x\) for \(0 \leq x \leq 2\).
- **D. (√2,√2) only**: Incorrect. While (√2,√2) lies on the circle, it does not lie on the line \(y = x\) for the specified range.
### Summary of the Correct Answer
The correct answer is **A. (1,1) only**.
### Revision Summary
- The predator moves in a circle defined by \(x^2 + y^2 = 2\).
- The prey moves along the line \(y = x\) for \(0 \leq x \leq 2\).
- The intersection point found is (1,1), which is valid within the prey's movement range.
- Other options either include points outside the valid range or points that do not satisfy both equations.