# NCERT Solutions for Class 10 Maths Chapter 9 Exercise 9.1

NCERT Solutions for Class 10 Maths Chapter 9 Exercise 9.1 Some Applications of Trigonometry in PDF form free download Hindi Medium and English Medium or View in Video Format updated for academic session 2020-21.

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Class: | 10 |

Subject: | Maths – गणित |

Chapter 9: | Exercise 9.1 |

### 10 Maths Chapter 9 Exercise 9.1 Solutions

NCERT Solutions for Class 10 Maths Chapter 9 Exercise 9.1 Some Applications of Trigonometry – Height and Distance questions in PDF form to free download and for online use also, updated for new academic session 2020-21. Visit to Class 10 Maths Chapter 9 main page for other exercises whether download or online study.

#### Questions for Practice with Answers

1. An aeroplane, when 3000 m high, passes vertically above another plane at an instant when the angle of elevation of two aeroplanes from the same point on the ground are 60° and 45° respectively. Find the vertical distance between the two planes. [Answer: 1268 m]

2. The angle of elevation of a cloud from a point 60 metres above a lake is 30° and the angle of depression of its reflection of the cloud in the lake is 60°. Find the height of the cloud. [Answer: 120 m]

3. A bird is sitting on the top of a tree, which is 80 m high. The angle of elevation of the bird, from a point on the ground is 45°. The bird flies away from the point of observation horizontally and remains at a constant height. After 2 seconds, the angle of elevation of the bird from the point of observation becomes 30°. Find the speed of flying of the bird. [Answer: 29.28 m]

4. From the top of a 7 m high building, the angle of elevation of the top of the tower is 60° and the angle of depression of the foot of the tower is 30°. Find the height of the tower. [Answer: 28 m]

##### Frequently Asked Questions with Answers

1. A boy standing on a horizontal plane finds a bird flying at a distance of 100 m from him at an elevation of 30°. A girl, standing on the roof of 20 m high building, finds the angle of elevation of the same bird to be 45°. Both the boy and girl are on the opposite sides of the bird. Find the distance of bird from the girl. [Answer: 30√2 m]

2. Anand is watching a circus artist climbing a 20m long rope which is tightly stretched and tied from the top of vertical pole to the ground. Find the height of the pole if the angle made by the rope with the ground level is 30°. [Answer: 10 m]

3. From the top of a hill, the angles of depression of two consecutive kilometre stones due east are found to be 30° and 45°. Find the height of the hill. [Answer: 1.37 km]

4. The string of a kite is 150 m long and it makes an angle 60° with the horizontal. Find the height of the kite above the ground. (Assume string to be tight). [Answer: 75√3]

5. The upper part of a tree broken over by the wind makes an angle of 30° with the ground and the distance of the root from the point where the top touches the ground is 25 m. What was the height of the tree? [Answer: 43.3 m]

###### Questions from the Board Papers

1. A vertical flagstaff stands on a horizontal plane. From a point 100 m from its foot, the angle of elevation of its top is found to be 45°. Find the height of the flagstaff. [Answer: 100 m] 15. The shadow of a vertical tower on level ground increases by 10 m when the altitude of the sun changes from 45° to 30°. Find the height of the tower. [Answer: 13.65 m]

2. An aeroplane at an altitude of 200 m observes angles of depression of opposite points on the two banks of the river to be 45° and 60°, find the width of the river. [Answer: 315.8 m]

3. A fire in a building ‘B’ is reported on telephone in two fire stations P an Q, 20 km apart from each other on a straight road. P observes that the fire is at an, angle of 60° to the road, and Q observes, that it is at an angle of 45° to the road. Which station should send its team and how much distance will this team has to travel? [Answer: Station P, 14.64 km]

4. A 1.2 m tall girl spots a balloon on the eve of Independence Day, moving with the wind in a horizontal live at a height of 88.2 m from the ground. The angle of elevation of the balloon from the girl at an instant is 60°. After some time, the angle of elevation reduces to 30°. Find the distance travelled by the balloon. [Answer: 58√3 m]

###### Important Questions for Practice

1. As observed from the top of a light house, 100 m high above sea level, the angle of depression of a ship, sailing directly towards it, changes from 30° to 60°. Determine the distance travelled by the ship during the period of observation. [Answer: 115.5 m]

2. The angles of elevation and depression of the top and bottom of a light house from the top of a building 60 m high are 30° and 60° respectively. Find (i) The difference between the height of the light house and the building. (ii) distance between the light house and the building. [Answer: 20 m, 34.64 m]

3. The angles of elevation of the top of a tower from two points on the ground at distances 9 m and 4 m from the base of the tower are in the same straight line with it are complementary. Find the height of the tower. [Answer: 6 m]

4. A man standing on the deck of a ship, 10 m above the water level observes the angle of elevation of the top of a hill as 60° and angle of depression the bottom of a hill as 30°. Find the distance of the hill from the ship and height of the hill. [Answer: 40 m, 17.32 m]

###### Common Questions in all Exams

1. A 7 m long flagstaff is fixed on the top of a tower on the horizontal plane. From a point on the ground, the angle of elevation of the top and the bottom of the flagstaff are 45° and 30° respectively. Find the height of the tower. [Answer: 9.6 m]

2. The angle of elevation of a tower at a point is 45°. After going 40 m towards the foot of the tower, the angle of elevation of the tower becomes 60°. Find the height of the tower. [Answer: 94.8 m]