Chapter 16 II Earth as a Sphere ENHANCE

CHAPTER 16: EARTH AS A SPHERE

Important Notes:

The distance between two points on the surface of the Earth is the length of the arc connecting the two places.

This distance (on the earth) is usually measured in nautical miles (n.m.) The shortest distance from one point to another point on the surface of the earth is along the great

circle.

Distance DE = nautical miles

Distance FG = nautical miles

Distance JK = nautical miles

The distance along the longitude = the difference between two latitudes 60 n.m. The distance along a parallel of latitude = the difference between two the two longitudes 60 cos 0 n.m.

Example:

Earth As A Sphere 1

θ

θ0 N

AB = = 3600 n.m.

PQ = = 7800 n.m.

AC = = 600 n.m.

CP A

600 N

1000 E

S

N

O

Q

B

●

●

800 E

X ●

700S

●

●

●

00

16.1 The Distance Along The Surface of the Earth (Along The Meridian)

1. (a) Ex : Calculate the distance of PQ

The difference between two latitudes = 670 – 450

= 220

The distance of PQ = 22 60’ = 1320 n.m

(Now YOU try……)

b) Find the distance PQ

2. (a) Ex : Calculate the distance of PQ

The difference between two latitude = 700 -00 = 700


b) Given the distance of QR is 6600 b.n. Find the latitude of R.

The difference between the two latitudes

=

= 1100

The latitude of R = 1100 – 700

= 400 S

Earth As A Sphere 2

720 N

230 S

P

Q

670 N

450 N

P

Q

O

220

N

S

N

Q

O

700 N

R

O0

P

S

3.

(a) Calculate the distance AB

b) Given the distance of AC is 9000 nm, find the latitude of C.

4.

a) Given the distance PQ is 2700 n.m. and P (0, 900W), find the latitude of Q

b) Given PQ = PR, find the latitude of R.

Earth As A Sphere 3

S

R

Q

O0

N

P

700 N

500 N

N

S

B

A

C

5.

(a) Given POR = 1100, PQ = QR. Find the distance of PQ.

b) State the latitude of P and R.

Latitude of P =

Latitude of R =

6. P(100 N, 800 E), Q and R are three points on the earth surface. Q lies on to the north of P and R lies on to the south of P.

a) The distance of PQ along the meridian is 2700 nm. Find the latitude of Q.

b) The distance of PR along the meridian is 1920 nm. Find the latitude of R.

Earth As A Sphere 4

P

R

O1100

Q00

16.2 The Distance on the Surface of the Earth (Along The Equator)

1. Calculate the distance of PQ

(a)

The difference between two latitudes = 450 – 100

= 350

The distance PQ = 35 60 = 2100 n.m

b) Find the distance PQ:

c) P (00, 700 W) , Q (00, 120 E)

d) P (00, 320 E) , Q (00, 400 W)

e) P (00, 70030’ E) , Q (00, 290 30’ W)

Earth As A Sphere 5

230 E

P

230 W

Q 00

QP

100 W450 W

2.

a) Calculate the distance of PQ

The difference between two longitudes = 800 + 100

= 900


b) Given PR = 3120 n.m Find the longitude of R The difference between longitudes P and R

=

= 520

Longitude of R = 100 + 520 = 620 E

3.

a) Given P (00, 100 E) and R (00, 100 W), calculate the distance from P to R.

b) The distance of PQ along the equator is 2400 nautical miles. Find the longitude of Q.

Earth As A Sphere 6

U

O

100 E

P

QR

S800 W

U

O

100 E

PQ

R

S100 W

4.

a) Calculate the distance PQ.

b) Given PR = PQ, find the longitude of R.

5.

a) The distance of PQ along the equator is 900 nautical miles. Find the longitude of Q.

b) Given the distance of PR = 2PQ. Find the longitude of R.

Earth As A Sphere 7

U

O

1000 E

P QR

S100 E

00

U

O

PQ

R

S250 W

00

6. Given P (00, 250 E), Q lies in the east of P and R lies on the west of P.

a) The distance of PQ along the equator is 1920 nautical miles. Calculate the longitude of Q.

b) Given PR = PQ, calculate the distance

of QR.

16.3 The Distance Along The Surface of the Earth (Along The Common Parallel Of Latitude)

1. a) Calculate the distance of PQ.

The difference of two longitudes = 550+ 300

= 850

The distance of PQ = 85 60’ kos150 = 4926.09 n.m

b)

Earth As A Sphere 8

230 E

Q

Q (150 S, 550 W)

P(150 S, 300 E)

Q (100 S, 100 W)

P(100 S, 00)

c) P (500 N, 300 W), Q (500 N, 400 E)

d) P (400 S, 250 W), Q (400 S, 790 E)

e) P (160 S, 100 30’ E), Q (160 S, 210 30’ W)

2.

a) Find the distance of PQ. The difference between of P and Q longitude = 700 - 200 = 500

The distance of PQ = 50 60 cos 600

= 1 500 n.m

b) Given PR = 4 200 nautical miles. Find the longitude of R.

4 200 = the difference between two longitude 60 cos 600

The difference between two longitude

= =

1400

find the longitude of R. = 1400 - 200

= 1200 E

Earth As A Sphere 9

200 W

700 W

N

Q 600 N

P R

S

3.

a) Find the distance of PQ.

b) Given PR = 1200 nautical miles, find the longitude of R.

4.

a) Find the distance of PQ.

b) Given PR = 2PQ, find the longitude of R.

Earth As A Sphere 10

200 W

450 W

N

Q 700 N

P R

S

N

100 W

Q450 SP R

S500E

5.

a) Given PQ = 1234 nautical miles. Find the longitude of Q.

b) Given the longitude of R is 1000 W. Find the distance of QR.

6. Given P (750 N, 420 E), Q (750 N, 420 W) and R lies in between PQ with PR = QR

a) Find the position of R.

b) Find the distance of PR measured along the common parallel latitude.


N

Q

00

PR

S

200

300W

O

16.4 The shortest distance (is always the distance along the great circles)

Find the shortest distance between P and Q.

1.

POQ = 1800 – (500 + 500) = 800

Distance = 80 60 = 4800 n.m

The shortest distance between P and Q = 4800 n.m

2.

3. 4.


1700 E100 W

N

Q500 N

P

S

O

1700 E100 W

N

Q

700 NP

S

500 N

00

300 E400 S

N

Q

400 N

P

S

●

●

N

P Q

S250 W

● ●

Find the shortest distance between P and Q. (You are advised to sketch a diagram)

5. P (400 S, 1000 W), Q (400 S, 800 E) 6. P (100 S, 700 W), Q (350 S, 1100 E)

7. P (00, 1100 W), Q (00, 100 E) 8. P (400 N, 500 W), Q (400 S, 1300 E)


Questions based on the examination format (Paper 2)

1. F (400 S, 720 E), G (400 S, 100 W), H and J are four points on the surface of the earth. FH is the diameter of the earth and J is located at a distance of 3780 nautical miles due north of F. (a) State the position of H [1marks] (b) Calculate the latitude of J [2 marks] (c) Calculate the distance, in nautical miles from G eastwards to F, measured along

the common parallel of latitude. [5 marks]

(d) An aeroplane took off from G and flew due east to F and then due north to J. The average speed of the aeroplane for the whole flights is 500 knots, find the time of flight. [4 marks]

2. P (00, 720 E), Q and R are three points on the surface of the earth. Q is due south of P and QR is the diameter of the parallel of latitude 200 S.

(a) Mark the position of P on the diagram above. [1 mark] (b) State the longitude of R [2 marks]

(c) Calculate the shortest distance, in nautical miles, from Q to R, measured along the surface of the earth. [3 marks]

(d) An aeroplane took off from P and flew due south to Q and then due west to R. The average speed of its flight is 560 knots. Calculate

(i) the total distance, in nautical miles, travelled by the aeroplane,(ii) the total time, in hours taken by the aeroplane for the whole flight

[6 marks]

3. P (500 N, 800 E), Q (500 N, 100 W) and R are three points on the surface of the earth.

(a) Calculate the shortest distance, in nautical miles, from P to the North Pole measured along the surface of the earth. [3 marks

(b) Given that R is 3620 nautical miles due south of Q. Calculate the latitude of R [4 marks]


Equator

R

S

N

Q

O

(c ) An aeroplane took off from P at 0630 and flew westwards to Q along the common parallel of latitude. The average speed of the flight is 350 knots. Calculate the time of the aeroplane landed at Q. [5 marks]

4. F (00, x0 W), G (00, 600 E), H (460S, 600 E) and J (460S, 850 E) are four points on the surface of the earth.

(a) Given that distance from F eastwards to G measured along the equator is 7920 nautical miles. Find the value of x. [4 marks]

(b) An aeroplane took off from G and flew due south to H. Given that the whole

flight took 4 hours, calculate the average speed, in knots, of the aeroplane.

[4 marks] (c) Another aeroplane took off from J at 1300, flew eastwards to H with an average

speed of 760 knots. Calculate its time of arrival at H. [4 marks] :

5. A (400 S, 300 W), B (400 S, 500 E) and C are three points on the earth‘s surface. AC is the diameter of a parallel of latitude.

(a) State the longitude of C. [1 marks] (b) Calculate (i) the distance, in nautical miles, from A eastwards to B, measured along the common parallel of latitude. (ii) the shortest distance, nautical miles, from A to C via South Pole. [6 marks] (c) An aeroplane took off from B and flew due north with an average speed of 570

knots. Calculate its latitude after flying 10 hours. [5 marks]

6. P and Q are two points on the surface of the earth with latitudes 400 N. Longitudes of P and Q are 200 E and 1600 W respectively.

(a) Calculate the distance, nautical miles, from P to Q, measured along the common parallel of latitude. [3 marks]

(b) An aeroplane took off from P and flew to Q at an average speed of 500 knots via the North Pole. Calculate

(i) the distance travelled by the aeroplane,(ii) the time taken of the whole flight

[4 marks](c) Another aeroplane took off from P and flew due west to Q half an hour after the

first aeroplane took off. Given that both of the aeroplanes reach Q at the same time, calculate the average speed, in knots, of the second aeroplane.

[5 marks]


7.

In the diagram above, positions of A, B, C and D are

and respectively.

(a) Calculate the shortest distance, in nautical miles,

(i) between A and B as measured along the common parallel of latitude,(ii) between B and C as measured along the meridian. [7 marks]

(b ) An aeroplane X took off from B and flew due east to A with an average

speed of 400 knots. At the same time, another aeroplane Y took off from D and flew due south to A with an average speed of 600 knots. Find the distance of aeroplane Y from A when aeroplane X reached A.

[5 marks]

8. P, Q and R are three points on the surface of the earth. PQ is the diameter of the parallel of latitude and PR is the diameter of the earth. The longitude of R is

a) Find i) the latitude of R

ii) the longitude of Pb). Find the distance, in nautical miles, from P due east to Q measured along the common parallel of latitude.c) An aeroplane flew from P towards Q passing through the North Pole. The

aeroplane started from P at 0900 hours and arrived at Q at 1530 hours on the same day. Find the average speed, in knots, of the aeroplane.

[50oS, 105oW; 6942 nm; 738.5 knots]


00

S

N

B

O

CD

A

9. Points , , C and D are four points on the surface of the

earth. Point C lies to the north of A and AD is the diameter of the earth.a) State the location of Db) Given that the distance between A and C, measured along the meridian, is 4020

nautical miles, find the latitude of C.c) Find the distance, in nautical miles, from B due west to A, measured along the

common parallel of latitude. d) An airplane took off from B at 0700 hours and flew due west to A along the

common parallel of latitude, then due north to C. If the airplane reached C at 1924 hours, find the average speed for the whole flight.

[(43oN, 102oE); 24oN; 4037 nm; 650 knots]

10. , F, G and H are four points on the surface of the earth. E, F and G lie of

the common parallel of latitude, such that EF is the diameter of that common parallel of latitude. The longitude of G is 47oW and H lies to the north of G.d) Find the longitude of F.e) An aeroplane took off from E and flew due west to G. Then, the aeroplane flew

due north to H which is 5100 nautical miles from G. The average speed of the aeroplane from E to H is 680 knot.

Calculatei) the latitude of Hii) the distance, in nautical miles, from E to Giii)the time, in hours, taken for the flight from E to H.

[117oW; 350N; 4242.48 nm; 13.74 hours]

11. K, L and M are three points on the surface of the earth on the parallel of latitude . The longitude of K is whereas the longitude of L is . Given KM is the diameter of the parallel of latitude .Find

a) the longitude of M.b) the shortest distance, in nautical miles, between K and M measured along the

surface of the earth.c) the distance, in nautical miles, from K to L measured along the parallel of

latitude.d) the duration of the flight from L to the North Pole, along the shortest distance by

an aeroplane at an average speed of 700 knots.[120oW; 4080 nm; 1678 nm; 12 hours 31 minutes]

12. and B are two points on the earth’s surface such that AB is a diameter of a

parallel of latitude.a) Find the longitude of Bb) AC is a diameter of the earth. On a diagram, mark the positions of A, B and C.

Hence, state the latitude and longitude of C.c) Calculate the shortest distance, in nautical miles, from B to the North Pole.


d) An aeroplane took off from A and flew due west along its parallel of latitude at an average speed of 540 knots. The aeroplane took 6 hours to reach a point X. Calculate

i. the distance, in nautical miles, from A to X,ii. the longitude of X.

[162oN; C (71oS, 162oW); 1140 nm; 3240 nm, 147o52’W]

13. , L and M are three points on the earth’s surface. KL is a diameter of

the parallel of latitude M is 4860 nautical miles due north of K.a) State the longitude of L.b) Find the latitude of M.c) Calculate the distance, in nautical miles, from K to L measured along the parallel

of latitude.d) An aeroplane flew from L to K using the shortest route measured along the

earth’s surface and then flew due north to M. Given that the average speed for the whole flight is 630 knots, calculate the total time of flight.

[100oW; 31oN; 6942.1 nm; 15 hours 20 minutes]

14. and B are two points on the equator while C and D are two points on th

common parallel of latitude. C and D lie due north of A and B respectively.a) Given that the distance from A to C, measured along the meridian, is 3360

nautical miles, find the latitude of C.b) Given that the longitude of D is 42oW, calculate the distance from C due west to

D, measured along the common parallel of latitude.c) An aeroplane took off from C and flew along the shortest route to D, then, due

south to B. If the average speed of the aeroplane for the whole flight was 550 knot, calculate i) the total distance coveredii) the time taken for the whole flight

[56oN; 2214.4 nm; 7440 nm; 13 hours 32 minutes]

15. , and C are three points on the surface of the earth

and AC is the diameter of the common parallel of latitude. a) (i) Find the longitude of C (ii) Find the difference, in nautical miles, between the distance fro A to C via

the North Pole and the distance from A to C via the South Pole.(iii) Calculate the distance, in nautical miles, from A due west to B, measured

along the common parallel of latitude.b) Calculate the latitude of a point, D, which lies 4110 nautical miles due

north of B.[140oW; 7200 nm; 6235.4 nm; 38o30’N]


16. P, Q, R and V are four points on the Earth’s surface. The longitude of Q and R are 50oW and 110oW respectively. Q and R are due east of P on the latitude 58oN such that PQ = QR. Point V which is on the latitude 76oN is due north of R.

a) Find the longitude of P. b) Calculate, in nautical miles,

i) the distance, measured along their common latitude, from Q due east to R.ii) the shortest distance, measured along the earth’s surface, from R due

north to V c) An aeroplane flying at an average speed of 600 knots, flew due east from Q to R

and then flew due north from R to V. Calculate to the nearest hour, the total time taken for the whole journey.

[10oW; 1908 nm; 1080 nm; 5 hours]

17. Two aeroplanes took off from an airport at and flew to their

destinations at an average speed of 600 knots. The first aeroplane flew due west and

arrived at B after flying of the circumference of the parallel of latitude 40oN. The

second aeroplane used the shortest route to arrive at .

a) Find the longitude of B.b) D is another point on the earth’s surface such that CD is a diameter of the

earth. Find the latitude of D.c) Calculate

i) the distance each aeroplane travelled in nautical miles.ii) the difference in time the two aeroplanes took for their respective flights.

[52oW; 20ON; 3309.3 nm and 9600 nm; 10 hours 29 minutes]


Past Year SPM Questions

Paper 2

1. November 2003 (Paper 2, Q 16) P (610 N, 100 E) and Q are two points on the surface of the earth such that PQ is the diameter of a parallel of latitude.

(a) Find the longitude of Q [1 mark]

(b) PR is the diameter of the earth. On the diagram below, mark the positions of Q and R.Hence, state the position of R.

[4 marks]

(c ) Calculate the shortest distance, in nautical miles, from Q to the North Pole. [2 marks]

(d) An aeroplane took off from P flew due west along its parallel of latitude with an average speed of 500 knots. The aeroplane took 9 hours to reach a point M. Calculate

(i) the distance in nautical miles, from P to M(ii) the longitude of M [5 marks]

2. July 2004 (Paper 2, Q 16)

, , R and V are four points on the surface of the earth. PR is a

diameter of the earth and V is located at a distance of 3060 nautical miles due north of Q.

(a) State the longitude of R. [2 marks]

(b) Calculate the latitude of V. [3 marks]

(c)Calculate the distance, in nautical miles, from P eastwards to Q, measured along the common parallel of latitude. [3 marks]

(d) An aeroplane took off from P at 0800 hours and flew due east to Q and then due north to V. Given that its average speed for the whole flight is 600 knots, at what time did the aeroplane arrive at V?

[4 marks]Earth As A Sphere 20

N

Equator

P

S

3. November 2004 (Paper 2, Q16)

P (600 S, 700 E), Q and R are three points on the surface of the earth. PQ is the diameter of the parallel of latitude 600 S. R lies 4 800 nautical miles due north of P.

(a) State the longitude of Q. [2 marks]

(b) Find the latitude of R. [3 marks]

(c) Calculate the distance, in nautical miles, from P to Q measured along the parallel latitude. [3 marks]

(d) An aeroplane took off from Q and flew towards P using the shortest distance, as measured along the surface of the earth, and then flew due north to R. Given that its average speed for the whole flight was 560 knots, calculate the total time taken for the flight. [4 marks]

4. July 2005 (Paper 2, Q16)

, G and H are three points on the surface of the earth. G is due north of F and

GH is the diameter of the parallel of latitude 30oN.

a. On Diagram 10 in the answer space, mark the position of F.[1 mark]

b. State the position of H.[2 marks]

c. Calculate the shortest distance, in nautical miles, from G to H measured along the surface of the earth.

[3 marks]d. An aeroplane took off from F and flew due north to G and then due east to H. The

average speed of the aeroplane is 500 knots. Calculatei) the total distance, in nautical miles, travelled by the aeroplanesii) the total time, in hours, taken by the aeroplane for the whole flight.

[6 marks]


N

Equator

H

S

G

DIAGRAM 10

5. November 2005 (Paper 2, Q 16) The table below shows the latitudes and longitudes of four points J, K, L and M, on the surface of the earth.

Point Latitude LongitudeJKLM

(a) P is a point on the surface of the earth such that JP is the diameter of the earth. State the position of P. [2 marks]

(b) Calculate(i) the value of x, if the distance from J to K measured along the meridian is 4200 nautical miles. (ii) the value of y, is the distance from J due west to L measured along the common parallel of latitude is 3270 nautical miles. [7 marks]

(c) An aeroplane took off from J and flew due west to L along the common parallel of latitude and then due south to M. If the average speed for the whole flight is 600 knots, calculate

the time taken for the whole flight. [3 marks]

6. July 2006 (Paper 2, Q16)

Diagram 8 shows the point and the point Q on the surface of the earth. The

point C is the centre of the common parallels of latitude of P and Q.

(a) State the position of Q [3 marks]

(b) R is a point on the surface of the earth. It is given that R is situated at a distance of 2400 nautical miles due south of P, measured along the meridian.


N

S

C

P

Q50O

DIAGRAM 8

Find the latitude of R. [4 marks](c) Calculate the distance, in nautical miles, from P due east to Q, measured along

the common parallels of latitude. [3 marks](d) An aeroplane took off from Q and flew due west to P along the common parallel

of latitude. Then, it flew due south, along the meridian, to R.

It is given that the total time taken for the flight is hours.

Calculate the average speed, in knots, of the aeroplane for the whole flight.[2 marks]

7. November 2006 (Paper 2, Q16)

Diagram 9 shows four points P, Q, R and X, on the surface of the earth. P lies on the longitude of . QR is the diameter of the parallel of latitude of X lies 5820 nautical miles due south of P.

(a) Find the position of R. [3 marks](b) Calculate the shortest distance, in nautical miles, from Q to R, measured along

the surface of the earth. [2 marks](c) Find the latitude of X. [3 marks](d) An aeroplane took off from P and flew due west to R along the parallel of latitude

with an average speed of 600 knots.Calculate the time, in hours, taken for the flight. [4 marks]


N

S

RP

Q

O

X

35O

50O

DIAGRAM 9

8 SPM Jul 2007. Q14 P (250 N , 600 E ), Q and R are three points on the surface of the earth. PR is the diameter of the earth. (a) State the longitude of R.

(b) PQ is the diameter of the parallel of latitude 250 N .

(i) State the position of Q .

(ii) Calculate the shortest distance, in nautical mile, from P to Q measured along the surface of the earth.

(c) An aeroplane took off from P and flew due west to Q along the common parallel of latitude and then flew due south to R. Calculate (i) the distance, in nautical miles, from P to Q measured along the common parallel of latitude. (ii) the time taken, in hours, for the whole flight if the average speed of the whole flight is 650 knots.


[2 marks]

[4 marks]

[6 marks]

9 SPM, Nov 2007 Q14 P (650 N , 400 W ), Q ( 650 N, 600 E ), R and V are four points on the surface of the earth. PR is the diameter of the parallel of latitude 650 N.

(a) (i) State the longitude of R.

(ii) Calculate the shortest distance, in nautical mile, from P to R measured along the surface of the earth.

(b) V lies south of Q and the distance VQ measured along the surface of the earth is 4500 nautical mile. Calculate the latitude of V .

(c) An aeroplane took off from P and flew due east to Q and then flew due south to V. The average speed for the whole flight was 550 knots. Calculate (i) the distance, in nautical miles, taken by the aeroplane from P to Q measured along the common parallel of latitude, (ii) the total time taken, in hours, taken for the whole flight .

10 SPM Jun 2008. Q16 P (250 N , 1200 E ), Q , R , M and V are five points on the surface of the earth. PQ is the diameter of the earth. R lies 2100 nautical miles along the common parallel of latitude due west of P.

(a) State the location of Q.

(b) Fine the longitude of R.

(c) PM is the diameter of the parallel latitude 50 N. Calculate the shortest distance, in nautical mile, from P to M , Measured along the surface of the earth.

(d) An aeroplane took off from P , flew due west to R , along the common parallel of latitude. Then it flew due south to V which lies due east of Q. It is given that the average speed of the whole flight is 560 knots.

Calculate the total time taken for the whole flight.


[4 marks]

[3 marks]

[5 marks]

[2 marks]

[4 marks]

[2 marks]

[4 marks]

11 SPM Nov 2008, Q16 P (53 N , 84 W ), Q (53 N, 25 W ) , R and V are four points on the surface of the earth. PR is the diameter of the parallel of latitude of 53 N.

(a) State the location of R.

(b) Calculate the shortest distance, in nautical mile, from P to R measured along the surface of the earth. (c) Calculate the distance, in nautical mile, from P due east to measured along the common parallel of latitude.

(d) An aeroplane took off from Q and flew due south to V . The average speed of the flight was 420 knots and the time taken

was hours .

Calculate

(i) the distance, in nautical mile, from Q to V measured along the meridian ,

(ii) the latitude of V .


[3 marks]

[2 marks]

[3 marks]

[4 marks]

ANSWERS

Past Year SPM Questions

1 Nov 2003 (a) 170 W (b) 61 S , 170 W (c) 1740 (d) (i) 4500 (ii) 147.7 W

2 Nov 2004 (a) 110 W (b) 20 N (c) 5400 (d) 15 hours

3 Nov 2005 (a) P(20 S , 155 W) (b) x = 50 , y = 33 (c) 10.45 hours

4 Nov 2006 (a) R(50 N , 135 E) (b) 4800 (c) 47 S (d) 9.32 hours

5 Jun 2007 (a) (i) 120 W (b) (i) Q (25 N , 120 W) (ii) 7800 n.m

(c) (i) 9788 n.m (ii) 19.67 hours

6 Nov 2007 (a) (i) 140 E , (ii) 3000 n.m (b) 10 S (c) 2535.71n.m (d) 12.79 hours

7 Jun 2008 (a) Q(50 S , 60 W ) (b) 65.55 E (c) 4800 n.m (d) 14.46 hours

8 Nov 2008 (a) (53 N, 96 E ) (b) 4440 (c) 2130.4 n.m (d) (i) 2730 n.m (ii) 7.5 N


Documents

Chapter 16 II Earth as a Sphere ENHANCE