21. The following figure shows the displacement time (x-t) graph of a body

The following figure shows the displacement time (x-t) graph of a body in motion. The ratio of the speed in first second and that in next two seconds is :

1 : 2
1 : 3
3 : 1
2 : 1
This question was previously asked in
UPSC CAPF – 2009
The correct option is D) 2 : 1.
The speed of the body is given by the magnitude of the slope of the displacement-time (x-t) graph.
In the first second (from t=0 to t=1), the displacement changes from 0 to 3. The velocity is `(3 – 0) / (1 – 0) = 3/1 = 3` units/second. The speed in the first second (v1) is `|3| = 3`.
In the next two seconds (from t=1 to t=3), the displacement changes from 3 to 0. The velocity is `(0 – 3) / (3 – 1) = -3/2` units/second. The speed in the next two seconds (v2) is `|-3/2| = 3/2`.
The ratio of the speed in the first second and that in the next two seconds is `v1 : v2 = 3 : (3/2)`. To express this ratio in integers, we can multiply both parts by 2: `(3 * 2) : (3/2 * 2) = 6 : 3`. Dividing by 3, we get the simplified ratio `2 : 1`.
The displacement-time graph provides information about the position of the body over time. Velocity is the rate of change of displacement, and speed is the magnitude of velocity. A positive slope indicates movement in one direction, while a negative slope indicates movement in the opposite direction. In this graph, the body moves from x=0 to x=3 in the first second and then back from x=3 to x=0 in the subsequent two seconds.

22. A square is drawn inside the circle as shown in the figure above. If t

A square is drawn inside the circle as shown in the figure above. If the area of the shaded portion is 32/7 units then the radius of the circle is :

√2 units
2 units
3 units
4 units
This question was previously asked in
UPSC CAPF – 2009
The correct option is B) 2 units.
The problem involves a square inscribed in a circle. Let the radius of the circle be `r`. The diameter of the circle is `2r`. When a square is inscribed in a circle, the diagonal of the square is equal to the diameter of the circle. Let the side of the square be `s`. The diagonal of the square is `s√2`. Thus, `s√2 = 2r`, which means `s = 2r/√2 = r√2`. The area of the square is `s² = (r√2)² = 2r²`. The area of the circle is `πr²`. The shaded portion is the area of the circle minus the area of the square. Given the area of the shaded portion is 32/7 units, we have `πr² – 2r² = 32/7`. Factoring out `r²`, we get `r²(π – 2) = 32/7`. Using the approximation `π ≈ 22/7`, we have `r²(22/7 – 2) = 32/7`. This simplifies to `r²((22 – 14)/7) = 32/7`, which is `r²(8/7) = 32/7`. Multiplying both sides by 7/8, we get `r² = (32/7) * (7/8) = 32/8 = 4`. Taking the square root, `r = √4 = 2` (since radius must be positive). The radius of the circle is 2 units.
For a square inscribed in a circle of radius `r`, the side length is `r√2` and the area is `2r²`. The ratio of the area of the inscribed square to the area of the circle is `2r² / (πr²) = 2/π`. The shaded area calculation relies on the difference between the circle’s area and the square’s area.

23. A person moves along a circular path by a distance equal to half the c

A person moves along a circular path by a distance equal to half the circumference in a given time. The ratio of his average speed to his average velocity is :

0.5
0.5π
0.75π
1.0
This question was previously asked in
UPSC CAPF – 2009
The correct option is B.
Let the circular path have radius R. The circumference is $C = 2\pi R$.
The distance covered by the person is half the circumference, $d = \frac{1}{2} C = \pi R$.
Let the time taken be $t$.
Average speed is defined as the total distance traveled divided by the total time taken.
Average speed = $\frac{d}{t} = \frac{\pi R}{t}$.

The person moves along a circular path by a distance equal to half the circumference. This means the person starts at one point on the circle and ends at the diametrically opposite point.
Let the starting point be A and the ending point be B, where AB is a diameter of the circle.
The displacement is the shortest straight-line distance from the initial position to the final position. In this case, the displacement is the length of the diameter.
Displacement = $2R$.

Average velocity is defined as the total displacement divided by the total time taken.
Average velocity = $\frac{\text{Displacement}}{t} = \frac{2R}{t}$.

The ratio of average speed to average velocity is:
Ratio = $\frac{\text{Average speed}}{\text{Average velocity}} = \frac{\pi R / t}{2R / t} = \frac{\pi R}{t} \times \frac{t}{2R} = \frac{\pi}{2}$.
The value $\frac{\pi}{2}$ is equivalent to $0.5\pi$.

This question highlights the difference between speed (scalar, based on distance) and velocity (vector, based on displacement). Distance is the path length, while displacement is the change in position vector. For motion along a curved path, the distance is generally greater than the magnitude of the displacement. For a half circle, the distance is $\pi R$ and the displacement magnitude is $2R$.

24. From the following Venn diagram identify the number of persons who are

From the following Venn diagram identify the number of persons who are either good speakers or post graduates or doctors.

6
7
15
22
This question was previously asked in
UPSC CAPF – 2009
The correct option is D.
The Venn diagram shows the number of persons in different categories and their overlaps.
Good Speakers (S) circle includes regions with numbers 3, 2, 4, 1.
Post Graduates (P) circle includes regions with numbers 5, 2, 4, 3.
Doctors (D) circle includes regions with numbers 4, 1, 3, 4.

The question asks for the number of persons who are either good speakers or post graduates or doctors. This corresponds to the union of the three sets (S $\cup$ P $\cup$ D).
The number of elements in the union of sets is the sum of the numbers in all the distinct regions covered by the circles.
These regions are:
– Only Good Speakers (S only): 3
– Only Post Graduates (P only): 5
– Only Doctors (D only): 4
– Good Speakers and Post Graduates only (S $\cap$ P only): 2
– Good Speakers and Doctors only (S $\cap$ D only): 1
– Post Graduates and Doctors only (P $\cap$ D only): 3
– Good Speakers, Post Graduates, and Doctors (S $\cap$ P $\cap$ D): 4

Total number of persons in the union = Sum of numbers in all these regions
Total = 3 + 5 + 4 + 2 + 1 + 3 + 4 = 22.

The question asks for the size of the union of the three sets. The Venn diagram provides the size of each disjoint region formed by the intersections of the sets. Summing the numbers in all regions within the circles gives the total number of elements in the union.

25. The following blocks are of the same material. Which is the heaviest o

The following blocks are of the same material. Which is the heaviest one ?

A
B
C
All equal
This question was previously asked in
UPSC CAPF – 2009
The correct option is C.
The blocks are of the same material, so their weight is directly proportional to their volume. The heaviest block is the one with the largest volume. We assume the blocks are made up of unit cubes based on the visible grid lines.
Block A: Appears to be a $2 \times 1 \times 1$ block. Volume $V_A = 2 \times 1 \times 1 = 2$ cubic units. (Composed of 2 unit cubes).
Block B: Appears to have a $2 \times 2$ base (4 unit cubes) and a $1 \times 1$ block (1 unit cube) stacked on top. Total volume $V_B = (2 \times 2 \times 1) + (1 \times 1 \times 1) = 4 + 1 = 5$ cubic units. (Composed of 5 unit cubes).
Block C: Appears to have an L-shaped base and a height of 2 units. The L-shaped base is a $2 \times 2$ square with a $1 \times 1$ corner removed, so the area of the base is $2 \times 2 – 1 \times 1 = 4 – 1 = 3$ square units. The height is 2 units. Total volume $V_C = \text{Area of base} \times \text{Height} = 3 \times 2 = 6$ cubic units. (Composed of 6 unit cubes).

Comparing the volumes: $V_A = 2$, $V_B = 5$, $V_C = 6$.
Block C has the largest volume (6 cubic units) and is therefore the heaviest.

Visualizing the blocks as being made up of unit cubes helps in calculating their volumes by counting or by using geometric formulas based on the apparent dimensions. Assuming uniformity of material implies constant density, so weight is proportional to volume.

26. The missing number in the following table is : 1 7 9 2 14

The missing number in the following table is :

179
214?
3105117
12
16
26
20
This question was previously asked in
UPSC CAPF – 2009
The correct option is D.
Let the numbers in the table be $C_1, C_2, C_3$ for columns and $R_1, R_2, R_3$ for rows.
The table values are:
$R_1: C_1=1, C_2=7, C_3=9$
$R_2: C_1=2, C_2=14, C_3=?$
$R_3: C_1=3, C_2=105, C_3=117$

Let’s look for a relationship between the columns within each row.
Observe $R_1$: $1, 7, 9$. $1^2 + 7 + 1 = 1 + 7 + 1 = 9$. So $C_1^2 + C_2 + C_1 = C_3$.
Observe $R_3$: $3, 105, 117$. Let’s test the same relationship: $3^2 + 105 + 3 = 9 + 105 + 3 = 117$. This relationship holds for R3 as well.
Let’s apply this relationship to $R_2$: $C_1=2, C_2=14$.
The missing number ($C_3$) should be $C_1^2 + C_2 + C_1 = 2^2 + 14 + 2 = 4 + 14 + 2 = 20$.

Matrix or table-based reasoning problems often involve arithmetic operations, sequences, or functional relationships between the numbers in rows or columns. Identifying the pattern from the given rows is crucial.

27. Which will be the next term in the following ? KPA, LQB, MRC, NSD,

Which will be the next term in the following ?
KPA, LQB, MRC, NSD, ………

OET
OTE
TOE
EOT
This question was previously asked in
UPSC CAPF – 2009
The correct option is B.
The series is KPA, LQB, MRC, NSD, …
Let’s examine the pattern of each letter position:
First letters: K, L, M, N, … These are consecutive letters in the English alphabet. The next letter is O.
Second letters: P, Q, R, S, … These are consecutive letters in the English alphabet. The next letter is T.
Third letters: A, B, C, D, … These are consecutive letters in the English alphabet. The next letter is E.
Combining the next letters for each position, we get OTE.
This type of pattern is common in letter series questions. Analyze the sequence formed by letters at the same position in each term.

28. If WOMAN is coded as 12345 and SERVANT is coded as 6789450, then VOTER

If WOMAN is coded as 12345 and SERVANT is coded as 6789450, then VOTERS will be coded as :

920786
902876
978206
972086
This question was previously asked in
UPSC CAPF – 2009
The correct option is A.
The coding is based on assigning a unique digit to each letter appearing in the given words.
From “WOMAN is coded as 12345”:
W -> 1
O -> 2
M -> 3
A -> 4
N -> 5

From “SERVANT is coded as 6789450”:
S -> 6
E -> 7
R -> 8
V -> 9
A -> 4 (Matches the code from WOMAN)
N -> 5 (Matches the code from WOMAN)
T -> 0

We need to find the code for “VOTERS”. We use the established codes for each letter:
V -> 9
O -> 2
T -> 0
E -> 7
R -> 8
S -> 6
Combining these, VOTERS is coded as 920786.

This is a direct substitution cipher where each letter is replaced by a specific digit. The key is built from the examples provided. It’s important to check for consistency in the codes for letters that appear in both example words (A and N).

29. ‘R’ walks 1 km. to east and then he turns to south and walks 5 km. Aga

‘R’ walks 1 km. to east and then he turns to south and walks 5 km. Again he turns to east and walks 2 km. After this he turns to north and walks 9 km. How far is he from his starting point ?

3 km.
4 km.
5 km.
7 km.
This question was previously asked in
UPSC CAPF – 2009
The correct option is C.
Let the starting point be the origin (0,0) on a 2D plane, with East along the positive x-axis and North along the positive y-axis.
1. R walks 1 km to the east: The position is (1, 0).
2. He turns to south and walks 5 km: South is in the negative y direction. The position becomes (1, 0 – 5) = (1, -5).
3. Again he turns to east and walks 2 km: East is in the positive x direction. The position becomes (1 + 2, -5) = (3, -5).
4. After this he turns to north and walks 9 km: North is in the positive y direction. The position becomes (3, -5 + 9) = (3, 4).

The final position is (3, 4) and the starting position is (0, 0).
The distance from the starting point is the straight-line distance between (0, 0) and (3, 4).
Using the distance formula: Distance = $\sqrt{(x_2 – x_1)^2 + (y_2 – y_1)^2}$
Distance = $\sqrt{(3 – 0)^2 + (4 – 0)^2} = \sqrt{3^2 + 4^2} = \sqrt{9 + 16} = \sqrt{25} = 5$ km.

This problem is a classic example of vector addition or displacement calculation. Each leg of the journey is a displacement vector. Adding the displacements (1,0), (0,-5), (2,0), (0,9) gives the total displacement vector (3,4). The distance from the start is the magnitude of the total displacement vector.

30. If Saturday falls four days after today which is 6th January, on which

If Saturday falls four days after today which is 6th January, on which day did the first of December of the previous year fall ?

Tuesday
Friday
Sunday
Monday
This question was previously asked in
UPSC CAPF – 2009
The correct option is C.
Today is 6th January. Saturday falls four days after today.
Day of 6th January + 4 days = Saturday.
Day of 6th January = Saturday – 4 days = Tuesday.
So, 6th January (of the current year) is a Tuesday.

We need to find the day of the week for 1st December of the previous year.
Let the current year be Y. We are finding the day of 1st December, Y-1.
The period is from 1st December, Y-1 to 6th January, Y.
Number of days in December Y-1 = 31 days.
Number of days in January Y up to 6th = 6 days.
Total number of days = 31 + 6 = 37 days.

To find the day of the week 37 days before Tuesday, we find the number of odd days in 37.
Number of odd days = $37 \pmod 7$.
$37 = 5 \times 7 + 2$. The remainder is 2.
So, 37 days is equal to 5 weeks and 2 days.
The day of 1st December, Y-1 is 2 days before Tuesday.
Tuesday – 1 day = Monday.
Monday – 1 day = Sunday.

To move backward in days, subtract the number of odd days from the current day of the week. To move forward, add the number of odd days. When calculating days across year boundaries, remember to account for the number of days in each month and whether the previous year was a leap year (although that is not relevant here as we only cross Dec and Jan).