A force is defined by the vector A= 3.5i- 1.5j+2.0k. What is the angle that the forces make with the positive y-axis? O 69.6° O 20 49

Structural Analysis
6th Edition
ISBN:9781337630931
Author:KASSIMALI, Aslam.
Publisher:KASSIMALI, Aslam.
Chapter2: Loads On Structures
Section: Chapter Questions
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### Problem Statement

A force is defined by the vector **A = 3.5i - 1.5j + 2.0k**. What is the angle that the forces make with the positive y-axis?

### Options

- **69.6°**
- **20.4°**
- **110°**
- **66.4°**

### Explanation

To solve this problem, you need to determine the angle between the vector **A** and the positive y-axis. This involves using the dot product and the magnitudes of the vectors.

1. **Vector Components**: 
   - **A = 3.5i - 1.5j + 2.0k**

2. **Dot Product Formula**: 
   \[
   A \cdot j = |A| \cdot |j| \cdot \cos(\theta)
   \]
   Since **j = 0i + 1j + 0k**:
   \[
   A \cdot j = -1.5
   \]

3. **Magnitude of Vector A**:
   \[
   |A| = \sqrt{(3.5)^2 + (-1.5)^2 + (2.0)^2}
   \]

4. **Solve for \(\theta\)**:
   \[
   \cos(\theta) = \frac{-1.5}{|A|}
   \]
   \[
   \theta = \cos^{-1}\left(\frac{-1.5}{|A|}\right)
   \]

After calculating, you'll find the correct angle from the available options.
Transcribed Image Text:### Problem Statement A force is defined by the vector **A = 3.5i - 1.5j + 2.0k**. What is the angle that the forces make with the positive y-axis? ### Options - **69.6°** - **20.4°** - **110°** - **66.4°** ### Explanation To solve this problem, you need to determine the angle between the vector **A** and the positive y-axis. This involves using the dot product and the magnitudes of the vectors. 1. **Vector Components**: - **A = 3.5i - 1.5j + 2.0k** 2. **Dot Product Formula**: \[ A \cdot j = |A| \cdot |j| \cdot \cos(\theta) \] Since **j = 0i + 1j + 0k**: \[ A \cdot j = -1.5 \] 3. **Magnitude of Vector A**: \[ |A| = \sqrt{(3.5)^2 + (-1.5)^2 + (2.0)^2} \] 4. **Solve for \(\theta\)**: \[ \cos(\theta) = \frac{-1.5}{|A|} \] \[ \theta = \cos^{-1}\left(\frac{-1.5}{|A|}\right) \] After calculating, you'll find the correct angle from the available options.
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