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From the top of a lamp post of height x ...

From the top of a lamp post of height x metres, two objects on the ground on the sameside of it ( and in line with the foot of the lamp post ) are observed at angles of depression of `30^(@)` and `60^(@)`, respectively. The distance between the objects is `32 sqrt( 3) `m. The value of x is `:`

A

54

B

48

C

45

D

36

Text Solution

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To solve the problem step by step, we will follow these instructions: ### Step 1: Understand the Problem We have a lamp post of height \( x \) meters. From the top of the lamp post, two objects on the ground are observed at angles of depression of \( 30^\circ \) and \( 60^\circ \). The distance between the two objects is \( 32\sqrt{3} \) meters. We need to find the height \( x \). ### Step 2: Draw a Diagram Draw a vertical line representing the lamp post. Label the top of the lamp post as point \( A \) and the foot of the lamp post as point \( B \). Let the two objects on the ground be points \( C \) and \( D \), with \( C \) being closer to the lamp post than \( D \). ### Step 3: Identify the Angles From point \( A \) (the top of the lamp post): - The angle of depression to point \( C \) is \( 60^\circ \). - The angle of depression to point \( D \) is \( 30^\circ \). ### Step 4: Set Up the Right Triangles Using the angles of depression, we can set up two right triangles: 1. Triangle \( ABD \) for angle \( 60^\circ \). 2. Triangle \( ABC \) for angle \( 30^\circ \). ### Step 5: Use Trigonometric Ratios For triangle \( ABD \): - The tangent of \( 60^\circ \) is given by: \[ \tan(60^\circ) = \frac{x}{y} \] where \( y \) is the distance from point \( B \) to point \( C \). Since \( \tan(60^\circ) = \sqrt{3} \), we have: \[ \sqrt{3} = \frac{x}{y} \implies y = \frac{x}{\sqrt{3}} \tag{1} \] For triangle \( ABC \): - The tangent of \( 30^\circ \) is given by: \[ \tan(30^\circ) = \frac{x}{y + 32\sqrt{3}} \] where \( y + 32\sqrt{3} \) is the distance from point \( B \) to point \( D \). Since \( \tan(30^\circ) = \frac{1}{\sqrt{3}} \), we have: \[ \frac{1}{\sqrt{3}} = \frac{x}{y + 32\sqrt{3}} \implies y + 32\sqrt{3} = \sqrt{3}x \tag{2} \] ### Step 6: Substitute Equation (1) into Equation (2) Substituting \( y = \frac{x}{\sqrt{3}} \) from equation (1) into equation (2): \[ \frac{x}{\sqrt{3}} + 32\sqrt{3} = \sqrt{3}x \] ### Step 7: Solve for \( x \) Rearranging gives: \[ 32\sqrt{3} = \sqrt{3}x - \frac{x}{\sqrt{3}} \] Multiplying through by \( \sqrt{3} \) to eliminate the fraction: \[ 32 \cdot 3 = 3x - x \] \[ 96 = 2x \] \[ x = \frac{96}{2} = 48 \] ### Final Answer The height of the lamp post \( x \) is \( 48 \) meters. ---
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