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All questions of Some Applications to Trigonometry for Class 10 Exam

 If the length of a shadow cast by a pole is  √3  times the length of the pole, then the angle of elevation of the sun is​
  • a)
    45°
  • b)
    60°
  • c)
    30°
  • d)
    90°
Correct answer is option 'C'. Can you explain this answer?

Anjana Khatri answered

Consider the height of tower be h

∴ height of shadow =√3h .

In a triangle ABC, 

tan ∠ACB = h / √3h

tan ∠ACB = 1 / √3

∠ACB = 30degree.

Therefore, angle of elevation is 30degree .

 If the angle of elevation of a cloud from a point 60 metres above a lake is 30o and the angle of depression of its reflection in the lake is 60°, then the height of the cloud above the lake is​
  • a)
    30 m
  • b)
    120 m
  • c)
    200 m
  • d)
    500 m
Correct answer is option 'B'. Can you explain this answer?

Neha Patel answered
Let AB be the surface of the lake and P be the point of observation such that AP = 60 m. Let C be the position of the cloud and C be its reflection in the lake.
Then CB = 
Draw PM⊥CB
Let CM = h
∴ CB = h + 60 m

The angles of elevation of the top of a tower from two points on the ground at distances 8m and 18m from the base of the tower and in the same straight line with it are complementary. The height of the tower is
  • a)
    8m
  • b)
    16m
  • c)
    12m
  • d)
    18m
Correct answer is option 'C'. Can you explain this answer?

Mysterio Man answered
Let AB= height of the tower=?,
and angle of elevations be ,
angle ACB =@ and angle ADB=90-@( as both the angles are complementary angles),
in right triangle ABC tan@=AB/BC,
tan@=AB/8---(1).,
in right triangle ABD tan(90-@)=AB/18,
we know that tan (90-@)=cot@,
so, cot@=AB/18,--(2),
Cot@=1/tan@,
from( 1)&(2),
AB/8=1/AB/18,
AB/8=18/AB,
AB²=18×8,
AB=√18×8=√3×3×2×2×2×2=3×2×2=12m

 The angle of elevation of the sun, when the length of the shadow of a tree is equal to the height of the tree, is:
  • a)
    45°
  • b)
    60°
  • c)
    30°
  • d)
    None of these
Correct answer is option 'C'. Can you explain this answer?

Ananya Das answered

Consider the diagram shown above where QR represents the tree and PQ represents its shadow
We have, QR = PQ
Let ∠QPR = θ
tan θ = QR/PQ = 1 (since QR = PQ)
⇒ θ = 45°
i,e., required angle of elevation = 45°

A tower stands vertically on the ground. From a point on the ground which is 25 m away from the foot of the tower, the angle of elevation of the top of the tower is found to be 45o. Then the height (in meters) of the tower is​
  • a)
    25
  • b)
    25√3
  • c)
    12.5
  • d)
    25√2
Correct answer is option 'A'. Can you explain this answer?

Vikram Kapoor answered

A point on the ground which is 25 m away from the foot of the tower i. BC= 25 m
Let the height of the tower be x
The angle of elevation of the tower is found to be 45 degree.i.e.∠ACB=45°
In ΔABC
Using trigonometric ratios

Hence the height of the tower is 25 m.

Tree is broken by the wind the top struck the ground at 30° at a distance of 30m. away from the root. Find the height of the tree.
  • a)
    45.9
  • b)
    88.60
  • c)
    54.63
  • d)
     51.96
Correct answer is option 'D'. Can you explain this answer?

Neha Patel answered
let , 
the height of standing part of the tree be = h 
the height of  fallen part (forms hypotenuse) be = x
then the total height of the tree will be = h + x 
now, 
tan 30 = h/30 m
     1/√3 = h/30 m 
    30/√3 = h
    ⇒ h= 30/√3 m           .... 1
similarly, 
cos 30 = 30 m/ x 
   √3/2 = 30 / x
√3x = (30)2 
 √3x = 60 m 
⇒ x = 60 / √3 m           ....2
       ( we now have both value of h and x )
   on adding equation1 & 2 :
 ⇒ h + x = 30 /√3 +60 /√3
         =90 /√3 m 
         = 60√3 m
so , the total height of the tree is 60√3 m .

A tree casts a shadow 4 m long on the ground, when the angle of elevation of the sun is 45o. The height of the tree is:​
  • a)
    5.2 m
  • b)
    4 m
  • c)
    3 m
  • d)
    4.5 m
Correct answer is option 'B'. Can you explain this answer?

In a triangle with one angle being 90 degrees (which the tree makes with the ground) and the other being 45 degrees (the angle of elevation), the 3rd angle is bound to be 45 degrees (180 - 90 - 45 = 45). 

We also know that sides opposite to equal angles are equal.

Hence, the height of the tree will also be 4m.

An observer 1.5 m tall is 28.5 m away from a tower. The angle of elevation of the top of the tower from his eyes is 45°. The height of the tower is​
  • a)
    10 m
  • b)
    40 m
  • c)
    30 m
  • d)
    20 m
Correct answer is option 'C'. Can you explain this answer?

Nk Classes answered
To solve for the height of the tower, we use the tangent function. The angle of elevation is 45°, and the horizontal distance from the observer to the tower is 28.5 m.
Let the height of the tower be h. The observer's eye level is 1.5 m, so the difference in height between the top of the tower and the observer's eyes is h−1.5h.

If the shadow of a boy ‘x’ metres high is 1.6m and the angle of elevation of the sun is 45°, then the value of ‘x’ is
  • a)
    2m
  • b)
    0.8m
  • c)
    3.6m
  • d)
    1.6m
Correct answer is option 'D'. Can you explain this answer?

Nk Classes answered
The given information indicates:
  • Height of the boy = x meters
  • Shadow length = 1.6 meters
  • Angle of elevation = 45 degrees
Using the trigonometric relation for a 45 degree angle 
Substitute the values:
Thus, the height of the boy is 1.6 meters.

A tree is broken by wind and its upper part touches the ground at a point 10 metres from the foot of the tree and makes an angle of 45° with the ground. The entire length of the tree is​
  • a)
    20 m
  • b)
    10(1+√2)m
  • c)
    10 m
  • d)
    10√2 m
Correct answer is option 'B'. Can you explain this answer?

Drishti Kumari answered
Base = 10m
Angle of elevation = 45 degree
tan 45 ^ = P / b ( Let p supoose h )
1= h / 10
h = 10 m
height of half tree = 10 m
Now the length of broken part i.e, hypotenuse
H^2 = P ^2 + B ^2
H ^2 = 10^2 + 10 ^2
H ^2 = 100 +100
H = root under 100
H = 10 root 2

Hence , the length of entire tree = 10 + 10 root2
10 ( 1 + root 2 )
That's why B is the correct optipn .

If the length of a shadow of a tower is increasing, then the angle of elevation of the sun is
  • a)
    neither increasing nor decreasing
  • b)
    decreasing
  • c)
    increasing
  • d)
    none of these
Correct answer is option 'B'. Can you explain this answer?

Nk Classes answered
As the length of the shadow of a tower increases, the sun moves closer to the horizon. This means the angle of elevation of the sun decreases because the angle between the line of sight to the sun and the ground becomes smaller.
Thus, the angle of elevation is decreasing.

If the altitude of the sun is 60°, the height of a tower which casts a shadow of length 90m is
  • a)
    60m
  • b)
    90m
  • c)
    60√3m
  • d)
    90√3m
Correct answer is option 'D'. Can you explain this answer?

We are given:
  • Angle of elevation (θ) = 60 degree 
  • Shadow length (L) = 90 m 
  • Height of the tower (h) needs to be calculated.
The relationship between the height of the tower (h) and the shadow length (L) is given by:

A kite is flying at a height of 200m above the ground. The string attached to the kite is temporarily tied to a point on the ground. The inclination of the string with the ground is 45°. The length of the string, assuming that there is no slack in the string is
  • a)
    100m
  • b)
    200m
  • c)
    100√2m
  • d)
    200√2m
Correct answer is option 'D'. Can you explain this answer?

Degrees.

To find the length of the string, we can use trigonometry.

Let's call the length of the string "x". We can use the tangent function to find x:

tan(45) = opposite/adjacent
tan(45) = 200/x

Now we can solve for x:

x = 200/tan(45)

Using a calculator, we find:

x ≈ 200

Therefore, the length of the string is approximately 200 meters.

 If the angles of depression from the top of a tower of height 40 m to the top and bottom of a tree are 45° and 60° respectively, then the height of the tree is
  • a)
  • b)
  • c)
  • d)
    None of the above
Correct answer is option 'B'. Can you explain this answer?

A tower of height 40 m is given, and the angles of depression from the top of the tower to:
  • The top of the tree = 45°
  • The bottom of the tree = 60°
We need to find the height of the tree (h).
Step 1: Use trigonometry for the angles of depression
Let:
  • The distance between the base of the tower and the base of the tree = d
  • The height of the tree = h
From the 45° angle (to the top of the tree):
The formula is:
tan(45°) = (Height of the tower - Height of the tree) / Distance (d)
Since tan(45°) = 1:
1 = (40 - h) / d
d = 40 - h (1)
From the 60° angle (to the bottom of the tree):
The formula is:
tan(60°) = Height of the tower / Distance (d)
Since tan(60°) = √3:
√3 = 40 / d
d = 40 / √3 (2)
Step 2: Solve the equations
Equate d from equations (1) and (2):
40 - h = 40 / √3
Rearrange to solve for h:
h = 40 - (40 / √3)
Rationalize the denominator:
h = 40 - (40√3 / 3)
h = (120 / 3) - (40√3 / 3)
h = (40 (3 - √3)) / 3
The height of the tree is:
b) (40 / 3) (3 - √3)

From a point P on the level ground, the angle of elevation of the top of a tower is 30°. If the tower is 100m high, the distance between P and the foot of the tower is
  • a)
    100√3m
  • b)
    200√3m
  • c)
    300√3m
  • d)
    150√3m
Correct answer is option 'A'. Can you explain this answer?

Let QR be the height of the tower, then QR = 100 mQ And angle of elevation of the top of the tower be ∠PPR = 30° 
Therefore, the distance between P and the foot of the tower is 100√3 metres.

If the length of the shadow of a tower is √3 times that of its height, then the angle of elevation of the sun is
  • a)
    30°
  • b)
    45°
  • c)
    60°
  • d)
    75°
Correct answer is option 'A'. Can you explain this answer?

Ananya Das answered
Let AB be the tree and AP be the shadow.
Let AB = x meters. Then AP = x√3 meters
Also ∠APB = θ
In right angled triangle ABP 

Therfore the angle of elevation of the Sun is 30°.

A contractor planned to install a slide for the children to play in a park. If he prefers to have a slide whose top is at a height of 1.5m and is inclined at an angle of 30° to the ground, then the length of the slide would be
  • a)
    1.5m
  • b)
    2√3m
  • c)
    √3m
  • d)
    3m
Correct answer is option 'D'. Can you explain this answer?

Nk Classes answered
We are given:
  • Height of the slide: h=1.5 m
  • Angle of inclination: θ=30
  • We need to find the length of the slide (l).
The relationship between the height (h), the length of the slide (l), and the angle of inclination (θ) is given by:
The length of the slide is 3 m.

If the length of the shadow of a tower is equal to its height, then the angle of elevation of the sun is
  • a)
    30°
  • b)
    45°
  • c)
    60°
  • d)
    65°
Correct answer is option 'B'. Can you explain this answer?

Om Khanna answered
Let AB be the tower and AC be its shadow 

And AB = AC= x m
Let the angle of elevation of the sun be θ.
Then ∠ACB = θ
In right angled triangle ABC 

Therefore, the angle of elevation of the Sun is 45°.

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