Angles of Elevation, Depression, and Bearings

13 questions

Question 1Question

A vessel departs from a harbor HH and sails 12 km12\text{ km} on a bearing of 040040^\circ to reach point AA. From point AA, it changes course and sails 5 km5\text{ km} on a bearing of 130130^\circ to reach point BB. What is the bearing of point BB from harbor HH, to the nearest degree?

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Answer: 063063^\circ

Answer

063063^\circ (or 063063^\circ to the nearest degree)
The navigation path forms a right-angled triangle at point AA because the reverse bearing of HH from AA (220220^\circ) differs from the bearing of BB from AA (130130^\circ) by exactly 9090^\circ. Using the right triangle trigonometric ratio tan(AHB)=512\tan(\angle AHB) = \frac{5}{12}, the angle AHB\angle AHB is found to be approximately 22.6222.62^\circ. Adding this angle to the initial bearing of 040040^\circ yields 062.62062.62^\circ, which rounds to 063063^\circ.

Step-by-Step Solution

1
Determine the back bearing of HH from AA and calculate the interior angle at AA.
Back bearing of HH from A=040+180=220A = 040^\circ + 180^\circ = 220^\circ. Interior angle HAB=220130=90\angle HAB = 220^\circ - 130^\circ = 90^\circ.
Knowing the directions of AHAH and ABAB allows us to find the interior angle of HAB\triangle HAB at point AA.
2
Calculate the interior angle AHB\angle AHB using right-triangle trigonometry.
\tan(\angle AHB) = \frac{AB}{HA} = \frac{5}{12} \implies \angle AHB = \arctan\left(\frac{5}{12}\right) \approx 22.62^\circ.
Since HAB\triangle HAB has a right angle at AA, tangent relates the opposite side AB=5 kmAB = 5\text{ km} to the adjacent side HA=12 kmHA = 12\text{ km}.
3
Calculate the total bearing of BB from HH.
\text{Bearing} = 040^\circ + 22.62^\circ = 062.62^\circ \approx 063^\circ.
The line HBHB lies to the right of line HAHA, so the interior angle AHB\angle AHB is added to the initial bearing of line HAHA (040040^\circ).

Key Concept

Bearings and Right-Angled Triangles
Estimated Time:1m 30s
Question 2Question

A boat sails 10 km10\text{ km} from a port PP on a bearing of 040040^\circ to a point QQ. From QQ, it changes direction and sails 103 km10\sqrt{3}\text{ km} on a bearing of 130130^\circ to reach a point RR. What is the bearing of port PP from point RR?

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Answer: 280280^\circ

Answer

The bearing of port P from point R is 280280^\circ.
By drawing North reference lines at P, Q, and R, the back bearing of P from Q is 040+180=220040^\circ + 180^\circ = 220^\circ. The bearing of R from Q is 130130^\circ, creating an interior right angle of 220130=90220^\circ - 130^\circ = 90^\circ at Q. Using right-triangle trigonometry, tan(QPR)=10310=3\tan(\angle QPR) = \frac{10\sqrt{3}}{10} = \sqrt{3}, giving QPR=60\angle QPR = 60^\circ. Adding this to the initial bearing of 040040^\circ gives the bearing of R from P as 100100^\circ. Finally, adding 180180^\circ gives the reverse bearing of P from R as 280280^\circ.

Step-by-Step Solution

1
Determine the interior angle PQR\angle PQR at vertex QQ
PQR=90\angle PQR = 90^\circ
The back bearing of P from Q is 040+180=220040^\circ + 180^\circ = 220^\circ. The bearing of R from Q is 130130^\circ. The interior angle between QP and QR is 220130=90220^\circ - 130^\circ = 90^\circ.
2
Calculate the angle QPR\angle QPR inside right-angled triangle PQRPQR
QPR=60\angle QPR = 60^\circ
Since triangle PQRPQR is right-angled at QQ, tan(QPR)=oppositeadjacent=QRPQ=10310=3\tan(\angle QPR) = \frac{\text{opposite}}{\text{adjacent}} = \frac{QR}{PQ} = \frac{10\sqrt{3}}{10} = \sqrt{3}. Therefore, QPR=arctan(3)=60\angle QPR = \arctan(\sqrt{3}) = 60^\circ.
3
Find the forward bearing of point RR from port PP
Bearing of RR from P=100P = 100^\circ
The bearing of Q from P is 040040^\circ. Since R lies to the right (clockwise) of segment PQ, add QPR=60\angle QPR = 60^\circ to 040040^\circ: 040+60=100040^\circ + 60^\circ = 100^\circ.
4
Compute the back bearing of port PP from point RR
Bearing of PP from R=280R = 280^\circ
The back bearing is obtained by adding 180180^\circ to the forward bearing from P to R: 100+180=280100^\circ + 180^\circ = 280^\circ.

Key Concept

Three-point bearing calculations using right-triangle trigonometry and back bearings
Estimated Time:2m 30s
Question 3Question

A forest ranger at a control post XX observes a lookout tower at point YY on a bearing of 072072^\circ. What is the bearing of the control post XX from the lookout tower YY?

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Answer: 252252^\circ

Answer

The bearing of the control post XX from the lookout tower YY is 252252^\circ.
The bearing of YY from XX is 072072^\circ. To find the bearing of XX from YY (the back bearing), we add 180180^\circ to the forward bearing because 072072^\circ is less than 180180^\circ. Calculation: 072+180=252072^\circ + 180^\circ = 252^\circ.

Step-by-Step Solution

1
Identify the forward bearing of point YY from point XX.
Forward bearing = 072072^\circ.
The question states that YY is observed from XX on a bearing of 072072^\circ.
2
Apply the rule for finding a back bearing when the forward bearing is less than 180180^\circ.
Back bearing = Forward bearing+180=072+180=252\text{Forward bearing} + 180^\circ = 072^\circ + 180^\circ = 252^\circ.
Since 072<180072^\circ < 180^\circ, we add 180180^\circ to determine the reverse direction from North at point YY.

Key Concept

Back Bearing / Reverse Bearing
Estimated Time:45s
Question 4Question

A surveyor stands at a point on level ground 50 m50\text{ m} away from the base of a vertical transmission tower. If the angle of elevation from the observer's position on the ground to the top of the tower is 4545^\circ, what is the height of the tower in meters?

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Answer: 50

Answer

The height of the transmission tower is 50 meters50\text{ meters}.
In a right-angled triangle, the tangent of the angle of elevation equals the ratio of the height (opposite side) to the horizontal distance (adjacent side). Since tan(45)=1\tan(45^\circ) = 1, the height of the tower must be equal to the horizontal distance of 50 m50\text{ m}.

Step-by-Step Solution

1
Formulate the trigonometric relationship using the right triangle formed by the observer, the base of the tower, and the top of the tower.
tan(45)=h50\tan(45^\circ) = \frac{h}{50}, where hh is the height of the tower.
The tangent ratio relates the opposite side (height of tower) to the adjacent side (distance along level ground).
2
Substitute the value of tan(45)=1\tan(45^\circ) = 1 and solve for hh.
h=50×1=50 mh = 50 \times 1 = 50\text{ m}.
Multiplying the adjacent side length by tan(45)\tan(45^\circ) yields the exact height.

Key Concept

Angle of elevation using basic right-triangle trigonometry
Question 5Question

A vertical tower TCTC of height hh metres stands on a horizontal plane with its base at CC. Point AA on the plane is due West of CC, and point BB is due South of AA, such that the distance AB=40 mAB = 40\text{ m}. If the angles of elevation of the top TT of the tower from AA and BB are 6060^\circ and 3030^\circ respectively, what is the height of the tower?

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Answer: 106 m10\sqrt{6}\text{ m}

Answer

The height of the tower is 106 m10\sqrt{6}\text{ m}.
Using the trigonometric tangent ratios, the horizontal distances from the base of the tower are AC=h3AC = \frac{h}{\sqrt{3}} and BC=h3BC = h\sqrt{3}. Because point AA is West of CC and point BB is South of AA, the angle CAB=90\angle CAB = 90^\circ. Applying Pythagoras' theorem BC2=AC2+AB2BC^2 = AC^2 + AB^2 yields 3h2=h23+16003h^2 = \frac{h^2}{3} + 1600, which simplifies to h=106 mh = 10\sqrt{6}\text{ m}.

Step-by-Step Solution

1
Express the horizontal distances ACAC and BCBC in terms of height hh.
In vertical right-angled triangle TACTAC, tan(60)=hAC    AC=h3\tan(60^\circ) = \frac{h}{AC} \implies AC = \frac{h}{\sqrt{3}}. In vertical right-angled triangle TBCTBC, \tan(30^\circ) = \frac{h}{BC} \implies BC = h\sqrt{3}$.
Relate the vertical height to the horizontal ground distances using tangent ratios.
2
Identify the geometry of the ground plane triangle CAB\triangle CAB.
Since AA is due West of CC and BB is due South of AA, the line segments CACA (East-West) and ABAB (North-South) are perpendicular. Thus, CAB\triangle CAB is right-angled at AA.
Cardinal directions (West and South from AA) are perpendicular to each other.
3
Apply Pythagoras' theorem to CAB\triangle CAB.
BC2=AC2+AB2    (h3)2=(h3)2+402    3h2=h23+1600BC^2 = AC^2 + AB^2 \implies (h\sqrt{3})^2 = \left(\frac{h}{\sqrt{3}}\right)^2 + 40^2 \implies 3h^2 = \frac{h^2}{3} + 1600.
Hypotenuse BCBC relates the two legs ACAC and ABAB on the horizontal plane.
4
Solve the equation for hh.
3h2h23=1600    8h23=1600    8h2=4800    h2=600    h=600=106 m3h^2 - \frac{h^2}{3} = 1600 \implies \frac{8h^2}{3} = 1600 \implies 8h^2 = 4800 \implies h^2 = 600 \implies h = \sqrt{600} = 10\sqrt{6}\text{ m}.
Simplify algebraic terms to determine hh in surd form.

Key Concept

Combining angles of elevation in 3D vertical planes with horizontal plane coordinate geometry and Pythagoras' theorem.
Question 6Question

A ship departs from a port PP and sails 10 km10\text{ km} on a bearing of 060060^\circ to reach a position QQ. From QQ, the ship changes course and sails 10 km10\text{ km} on a bearing of 150150^\circ to arrive at point RR. What is the bearing of point RR from point PP?

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Answer: 105105^\circ

Answer

The bearing of point RR from point PP is 105105^\circ.
The back bearing from position QQ to port PP is 240240^\circ. The difference between 240240^\circ and the new bearing of 150150^\circ yields an interior angle of 9090^\circ at vertex QQ. Since both distances PQPQ and QRQR are equal to 10 km10\text{ km}, triangle PQRPQR is a 45459045^\circ-45^\circ-90^\circ isosceles right triangle. Adding QPR=45\angle QPR = 45^\circ to the initial bearing of 060060^\circ yields a bearing of 105105^\circ for point RR from point PP.

Step-by-Step Solution

1
Determine the back bearing of PP from QQ.
The back bearing of PP from QQ is 060+180=240060^\circ + 180^\circ = 240^\circ.
To find the internal angle at QQ, we need the direction of PP relative to QQ.
2
Calculate the interior angle PQR\angle PQR.
PQR=240150=90\angle PQR = 240^\circ - 150^\circ = 90^\circ.
The difference between the line back to PP (240240^\circ) and the line to RR (150150^\circ) forms the interior angle at QQ.
3
Determine the properties of triangle PQRPQR and angle QPR\angle QPR.
Since PQ=QR=10 kmPQ = QR = 10\text{ km} and PQR=90\angle PQR = 90^\circ, triangle PQRPQR is an isosceles right triangle, so QPR=45\angle QPR = 45^\circ.
The two equal sides subtend equal acute angles in a right-angled triangle: (18090)/2=45(180^\circ - 90^\circ) / 2 = 45^\circ.
4
Calculate the total bearing of RR from PP.
Bearing of RR from P=060+45=105P = 060^\circ + 45^\circ = 105^\circ.
Point RR lies clockwise relative to the segment PQPQ, so we add QPR\angle QPR to the initial bearing of PQPQ.

Key Concept

Three-point bearing calculations using geometry of parallel lines and right-angled triangles.
Question 7Question

A forest ranger station YY is located on a bearing of 115115^\circ from an observation tower XX. What is the bearing of the observation tower XX from the forest ranger station YY?

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Answer: 295295^\circ

Answer

295295^\circ
The bearing of YY from XX is 115115^\circ. To find the bearing of XX from YY (the back bearing), add 180180^\circ to the forward bearing because 115<180115^\circ < 180^\circ. Calculating 115+180115^\circ + 180^\circ yields 295295^\circ.

Step-by-Step Solution

1
Identify the given forward bearing
The bearing of YY from XX is θ=115\theta = 115^\circ.
This is the initial directional angle measured clockwise from True North at point XX.
2
Calculate the back bearing of XX from YY
Back bearing =115+180=295= 115^\circ + 180^\circ = 295^\circ.
Because the forward bearing is less than 180180^\circ, the back bearing is obtained by adding 180180^\circ to find the opposite direction.

Key Concept

Back Bearing Calculation
Question 8Question

A vertical flagpole of height 15 m15\text{ m} standing on level ground casts a shadow of length 153 m15\sqrt{3}\text{ m}. Calculate the angle of elevation of the sun in degrees.

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Answer: 30

Answer

The angle of elevation of the sun is 30 degrees.
The tangent of the angle of elevation is given by the height divided by the shadow length, tanθ=15153=13\tan\theta = \frac{15}{15\sqrt{3}} = \frac{1}{\sqrt{3}}, which corresponds to an angle of 3030^\circ.

Step-by-Step Solution

1
Formulate the trigonometric relationship using the right triangle formed by the flagpole, the shadow, and the sunlight ray.
\tan\theta = \frac{\text{height of flagpole}}{\text{length of shadow}} = \frac{15}{15\sqrt{3}}
The tangent of an angle in a right-angled triangle is defined as the ratio of the opposite side to the adjacent side.
2
Simplify the ratio and evaluate the angle.
\tan\theta = \frac{1}{\sqrt{3}} \implies \theta = 30^\circ
The standard acute angle whose tangent value is 13\frac{1}{\sqrt{3}} is 3030^\circ.

Key Concept

Angle of Elevation and Trigonometric Ratios
Question 9Question

A search-and-rescue helicopter leaves a central station PP and flies 16 km16\text{ km} on a bearing of 050050^\circ to reach a waypoint QQ. It then changes course and flies 12 km12\text{ km} on a bearing of 140140^\circ to reach a mountain rescue site RR. From the central station PP, the angle of elevation to the helicopter hovering vertically above point RR is 4545^\circ. What is the vertical height of the helicopter above the horizontal plane of station PP, in kilometers?

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Answer: 20

Answer

The vertical height of the helicopter above the horizontal plane of station PP is 20 km20\text{ km}.
The horizontal journey forms a right-angled triangle PQRPQR with side lengths 16 km16\text{ km} and 12 km12\text{ km}, yielding a hypotenuse (horizontal distance PRPR) of 20 km20\text{ km}. Since the angle of elevation from PP to the hovering helicopter is 4545^\circ, the vertical height is equal to 20×tan(45)=20 km20 \times \tan(45^\circ) = 20\text{ km}.

Step-by-Step Solution

1
Find the back bearing of station PP from waypoint QQ
Back bearing = 050+180=230050^\circ + 180^\circ = 230^\circ
To determine the enclosed interior angle at point QQ, the reverse direction from QQ to PP must be calculated.
2
Calculate the interior angle PQR\angle PQR
\angle PQR = 230^\circ - 140^\circ = 90^\circ
Subtracting the forward bearing of RR from the back bearing of PP yields the right angle between the two paths.
3
Calculate the horizontal displacement distance PRPR
PR = \sqrt{16^2 + 12^2} = 20\text{ km}
Since PQR\triangle PQR is right-angled at QQ, the distance PRPR is obtained using the Pythagorean theorem.
4
Determine the vertical altitude using trigonometry
\text{Height} = PR \times \tan(45^\circ) = 20 \times 1 = 20\text{ km}
In the vertical right-angled triangle formed by PP, the ground projection of RR, and the helicopter, tan(45)=HeightHorizontal Distance\tan(45^\circ) = \frac{\text{Height}}{\text{Horizontal Distance}}.

Key Concept

Combining 3-point bearings in 2D with right-triangle trigonometry for 3D angles of elevation.
Question 10Question

An observer standing at the top of a vertical lighthouse observes two boats, XX and YY, on the surrounding horizontal sea surface. Boat XX lies due South of the lighthouse at an angle of depression of 3030^\circ, while boat YY lies due East of the lighthouse at an angle of depression of 4545^\circ. If the straight-line distance between boat XX and boat YY is 80 m80\text{ m}, what is the height of the lighthouse?

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Answer: 40 m40\text{ m}

Answer

The height of the lighthouse is 40 m40\text{ m}.
The height of the lighthouse is 40 m40\text{ m}. Since boat XX is due South and boat YY is due East, the line segments connecting the base of the lighthouse to each boat form a right angle (9090^\circ). Using basic trigonometry, the distance to boat XX is h3h\sqrt{3} and to boat YY is hh. Applying Pythagoras' theorem to the right triangle formed on the sea surface gives (h3)2+h2=802(h\sqrt{3})^2 + h^2 = 80^2, which simplifies to 4h2=64004h^2 = 6400, giving h=40 mh = 40\text{ m}.

Step-by-Step Solution

1
Express the horizontal distance from the lighthouse base LL to boat XX in terms of height hh.
LX=htan30=h3 mLX = \frac{h}{\tan 30^\circ} = h\sqrt{3}\text{ m}
The angle of elevation from boat XX to the top of the lighthouse is equal to the angle of depression (3030^\circ).
2
Express the horizontal distance from the lighthouse base LL to boat YY in terms of height hh.
LY=htan45=h mLY = \frac{h}{\tan 45^\circ} = h\text{ m}
The angle of elevation from boat YY to the top of the lighthouse is 4545^\circ.
3
Set up Pythagoras' theorem for right-angled triangle XLYXLY on the horizontal plane.
XY2=LX2+LY2    802=(h3)2+h2XY^2 = LX^2 + LY^2 \implies 80^2 = (h\sqrt{3})^2 + h^2
Boat XX is due South and boat YY is due East of the lighthouse base, making XLY=90\angle XLY = 90^\circ.
4
Solve the algebraic equation for hh.
6400=3h2+h2=4h2    h2=1600    h=40 m6400 = 3h^2 + h^2 = 4h^2 \implies h^2 = 1600 \implies h = 40\text{ m}
Dividing 64006400 by 44 gives 16001600, whose square root is 4040.

Key Concept

3D Geometry combining Angles of Elevation/Depression with Perpendicular Bearings
Question 11Question

A coastal monitoring station at point OO tracks two vessels on horizontal water. Vessel AA is located 15 km15\text{ km} from OO on a bearing of 070070^\circ, while Vessel BB is located 20 km20\text{ km} from OO on a bearing of 160160^\circ. What is the direct distance between Vessel AA and Vessel BB in kilometers?

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Answer: 25

Answer

The direct distance between Vessel A and Vessel B is 25 km.
The difference between the two bearings (160070=90160^\circ - 070^\circ = 90^\circ) establishes that triangle AOBAOB is a right-angled triangle at station OO. Applying Pythagoras' theorem yields AB=152+202=225+400=625=25 kmAB = \sqrt{15^2 + 20^2} = \sqrt{225 + 400} = \sqrt{625} = 25\text{ km}.

Step-by-Step Solution

1
Find the angle between the lines of sight to the two vessels
\angle AOB = 160^\circ - 070^\circ = 90^\circ
Subtracting the smaller bearing angle from the larger bearing angle from the same origin point gives the included angle.
2
Set up the equation for distance AB using Pythagoras' theorem
AB^2 = 15^2 + 20^2 = 225 + 400 = 625
Since the included angle is 90 degrees, the three points form a right-angled triangle where AB is the hypotenuse.
3
Calculate the principal square root of 625
AB = \sqrt{625} = 25\text{ km}
Taking the square root converts the squared distance into the direct linear distance between the vessels.

Key Concept

Calculating the distance between two points using bearings and right-angled triangle properties (Pythagoras' theorem).
Estimated Time:1m 30s
Question 12Question

A cargo ship departs from port MM and sails 24 km24\text{ km} on a bearing of 050050^\circ to reach point NN. From point NN, the ship changes course and sails 10 km10\text{ km} on a bearing of 140140^\circ to reach point PP. What is the direct distance, in kilometers, from port MM to point PP?

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Answer: 26

Answer

The direct distance from port M to point P is 26 km.
The back bearing from N to M is 230°, and the bearing from N to P is 140°. The interior angle at N is 230° - 140° = 90°. Using the Pythagorean theorem for the right triangle formed by M, N, and P, the direct distance is √(24² + 10²) = √676 = 26 km.

Step-by-Step Solution

1
Calculate the interior angle MNP\angle MNP at point NN
MNP=(050+180)140=230140=90\angle MNP = (050^\circ + 180^\circ) - 140^\circ = 230^\circ - 140^\circ = 90^\circ
The back bearing from NN to MM is 230230^\circ. Subtracting the forward bearing to PP (140140^\circ) gives the enclosed interior angle.
2
Apply the Pythagorean theorem to right-angled triangle MNPMNP
MP=MN2+NP2=242+102=576+100=676=26 kmMP = \sqrt{MN^2 + NP^2} = \sqrt{24^2 + 10^2} = \sqrt{576 + 100} = \sqrt{676} = 26\text{ km}
Because MNP=90\angle MNP = 90^\circ, triangle MNPMNP is a right-angled triangle with hypotenuse MPMP.

Key Concept

Bearings and Right-Angled Triangles
Question 13Question

A field surveyor starts at point PP and walks 10 km10\text{ km} due East to point QQ. From point QQ, she changes direction and walks 10 km10\text{ km} on a bearing of 210210^\circ to reach point RR. What is the bearing of point PP from point RR?

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Answer: 330330^\circ

Answer

The bearing of point PP from point RR is 330330^\circ.
Point QQ lies 10 km10\text{ km} East of PP (bearing 090090^\circ). From QQ, moving 10 km10\text{ km} on bearing 210210^\circ forms an interior angle of 6060^\circ with the line QPQP (which has bearing 270270^\circ). Because PQ=QR=10 kmPQ = QR = 10\text{ km} and the included angle is 6060^\circ, PQR\triangle PQR is equilateral, making QRP=60\angle QRP = 60^\circ. The back bearing from RR to QQ is 030030^\circ. Subtracting the 6060^\circ interior angle from 030030^\circ yields a bearing of 330330^\circ for point PP from point RR.

Step-by-Step Solution

1
Determine the interior angle PQR\angle PQR at point QQ.
PQR=60\angle PQR = 60^\circ
Since PP is due West of QQ, the bearing of PP from QQ is 270270^\circ. The bearing of RR from QQ is 210210^\circ. The interior angle between these two lines is 270210=60270^\circ - 210^\circ = 60^\circ.
2
Analyze the properties of triangle PQRPQR.
Triangle PQRPQR is an equilateral triangle with side lengths 10 km10\text{ km} and interior angles of 6060^\circ.
Given PQ=10 kmPQ = 10\text{ km} and QR=10 kmQR = 10\text{ km}, PQR\triangle PQR is isosceles. Since the vertex angle PQR=60\angle PQR = 60^\circ, the remaining two angles are also 6060^\circ each.
3
Calculate the back bearing of QQ from RR.
Bearing of QQ from RR is 030030^\circ.
The bearing of RR from QQ is 210210^\circ. The back bearing is 210180=030210^\circ - 180^\circ = 030^\circ.
4
Compute the bearing of PP from RR.
Bearing of PP from RR is 330330^\circ.
From line RQRQ (bearing 030030^\circ), line RPRP lies 6060^\circ counter-clockwise (since QRP=60\angle QRP = 60^\circ). Thus, 03060=30330030^\circ - 60^\circ = -30^\circ \equiv 330^\circ.

Key Concept

Bearings and Triangle Geometry