Lighthouse Angles
1. **Problem Statement:**
A lighthouse 50 m tall observes a ship moving from point P to Q. The angles of depression from the top of the lighthouse to the ship are 30° at P and 45° at Q. We need to find:
(i) Distance of the ship from the base of the lighthouse at Q.
(ii) Measures of angles \(\angle PBA\) and \(\angle QBA\).
(iii) (a) Distance traveled by the ship from P to Q.
(iii) (b) Speed of the ship from Q to A if it takes 10 minutes.
2. **Key Concepts and Formulas:**
- The angle of depression equals the angle of elevation from the ship to the lighthouse base.
- Using right triangle trigonometry, for height \(h=50\) m and horizontal distance \(d\), \(\tan(\theta) = \frac{h}{d}\).
- Speed formula: \(\text{speed} = \frac{\text{distance}}{\text{time}}\).
3. **Step (i): Distance at Q**
- Given angle of depression at Q is 45°.
- Using \(\tan 45^\circ = 1 = \frac{50}{d_Q} \Rightarrow d_Q = 50\) m.
4. **Step (ii): Angles \(\angle PBA\) and \(\angle QBA\)**
- By alternate interior angles, \(\angle PBA = 30^\circ\) and \(\angle QBA = 45^\circ\) (given angles of depression).
5. **Step (iii)(a): Distance traveled from P to Q**
- At P, angle of depression is 30°.
- \(\tan 30^\circ = \frac{50}{d_P} = \frac{1}{\sqrt{3}} \Rightarrow d_P = 50\sqrt{3} \approx 86.60\) m.
- Distance traveled = \(d_P - d_Q = 86.60 - 50 = 36.60\) m.
6. **Step (iii)(b): Speed from Q to A**
- Distance from Q to A is \(d_Q = 50\) m.
- Time = 10 minutes = \(\frac{10}{60} = \frac{1}{6}\) hours.
- Speed = \(\frac{50}{1000} \div \frac{1}{6} = 0.05 \times 6 = 0.3\) km/h.
**Final answers:**
(i) Distance at Q = 50 m.
(ii) \(\angle PBA = 30^\circ\), \(\angle QBA = 45^\circ\).
(iii)(a) Distance traveled = 36.60 m.
(iii)(b) Speed = 0.3 km/h.