Let $P_1: y = 4x^2$ and $P_2: y = x^2 + 27$ be two parabolas. If the area of the bounded region enclosed between $P_1$ and $P_2$ is six times the area of the bounded region enclosed between the line $y = \alpha x, \alpha > 0$ and $P_1$ then $\alpha$ is equal to:
Check Answer
Correct Answer: (D) 12
Explanation
Formula
Step-by-Step Derivation
- The equations of the parabolas are $P_1: y = 4x^2$ and $P_2: y = x^2 + 27$.
- First, find the points of intersection of $P_1$ and $P_2$:
- $$ 4x^2 = x^2 + 27 \implies 3x^2 = 27 \implies x^2 = 9 \implies x = \pm 3 $$
- The area $A_1$ enclosed by $P_1$ and $P_2$ is:
- $$ A_1 = \int_{-3}^{3} (x^2 + 27 - 4x^2) \, dx = 2 \int_{0}^{3} (27 - 3x^2) \, dx $$
- $$ A_1 = 2 \left[ 27x - x^3 \right]_{0}^{3} = 2(81 - 27) = 108 $$
- Next, find the points of intersection of $P_1$ and the line $y = \alpha x$:
- $$ 4x^2 = \alpha x \implies x = 0 \text{ or } x = \frac{\alpha}{4} $$
- The area $A_2$ enclosed by $P_1$ and $y = \alpha x$ is:
- $$ A_2 = \int_{0}^{\alpha/4} (\alpha x - 4x^2) \, dx = \left[ \alpha \frac{x^2}{2} - \frac{4x^3}{3} \right]_{0}^{\alpha/4} $$
- $$ A_2 = \alpha \left( \frac{\alpha^2}{32} \right) - \frac{4}{3} \left( \frac{\alpha^3}{64} \right) = \frac{\alpha^3}{32} - \frac{\alpha^3}{48} = \frac{\alpha^3}{96} $$
- We are given that $A_1 = 6 A_2$:
- $$ 108 = 6 \left( \frac{\alpha^3}{96} \right) \implies 18 = \frac{\alpha^3}{96} \implies \alpha^3 = 1728 $$
- Taking the cube root, we get $\alpha = 12$.
Final Answer
Therefore, the power of the lens is -2.0D (Option D).
Which of the following is a scalar quantity?
Check Answer
Correct Answer: (D) Electric Current
Explanation
Electric current has both magnitude and direction (flow of charges), but it does not obey the laws of vector addition. Hence, current is considered a scalar quantity.
What is the chemical formula of common rust?
Check Answer
Correct Answer: (A) Fe₂O₃ · xH₂O
Explanation
Rust is a hydrated iron(III) oxide with the formula Fe₂O₃ · xH₂O, formed by the reaction of iron, oxygen, and water.
The time period (T) of a simple pendulum is calculated using the formula:
Check Answer
Correct Answer: (A) T = 2π √(l/g)
Explanation
Pendulum Formula
Where:
- T = Time period (s)
- l = length of string (m)
- g = acceleration due to gravity (m/s²)
The formula holds true under small angular displacements.
A body of mass 5 kg is moving with a velocity of 10 m/s. A force is applied to it so that in 25 seconds, it attains a velocity of 35 m/s. What is the force applied?
Check Answer
Correct Answer: (B) 5 N
Explanation
Acceleration $a = \frac{v - u}{t} = \frac{35 - 10}{25} = 1 \text{ m/s}^2$.
Force $F = ma = 5 \times 1 = 5 \text{ N}$.
The work done in moving a charge of 2 C across two points having a potential difference of 12 V is:
Check Answer
Correct Answer: (B) 24 J
Explanation
Work done $W = qV = 2 \times 12 = 24 \text{ J}$.
This is the energy transferred when a charge moves through a potential difference.
What is the atomic number of an element whose electronic configuration is $2, 8, 7$?
Check Answer
Correct Answer: (C) 17
Explanation
Total electrons $= 2 + 8 + 7 = 17$. The element is Chlorine (Cl).
It belongs to Group 17 (halogens) and has 7 valence electrons, making it highly electronegative.
If $\sin\theta = \dfrac{3}{5}$, then the value of $\cos\theta$ is:
Check Answer
Correct Answer: (A) 4/5
Explanation
$\cos^2\theta = 1 - \sin^2\theta = 1 - \frac{9}{25} = \frac{16}{25}$
$\cos\theta = \frac{4}{5}$ (taking positive value for acute angle).
The pH of a neutral solution at 25°C is:
Check Answer
Correct Answer: (B) 7
Explanation
A neutral solution has equal concentrations of $\text{H}^+$ and $\text{OH}^-$ ions.
At 25°C, $[\text{H}^+] = 10^{-7}$ M, so pH $= -\log(10^{-7}) = 7$.
The acceleration due to gravity on the surface of the Moon is approximately:
Check Answer
Correct Answer: (C) 1.6 m/s²
Explanation
The Moon's gravitational acceleration is about $\frac{1}{6}$th of Earth's.
$g_{\text{moon}} \approx \frac{9.8}{6} \approx 1.63 \text{ m/s}^2 \approx 1.6 \text{ m/s}^2$.
The powerhouse of the cell is:
Check Answer
Correct Answer: (C) Mitochondria
Explanation
Mitochondria are called the "powerhouse of the cell" because they generate most of the cell's supply of adenosine triphosphate (ATP), used as a source of chemical energy.
They perform oxidative phosphorylation through the electron transport chain located in their inner membrane.
If $f(x) = x^3 - 3x^2 + 2$, then $f'(1)$ is equal to:
Check Answer
Correct Answer: (B) -3
Explanation
$f'(x) = 3x^2 - 6x$
$f'(1) = 3(1)^2 - 6(1) = 3 - 6 = -3$.
The SI unit of electric current is:
Check Answer
Correct Answer: (D) Ampere
Explanation
The Ampere (A) is the SI base unit of electric current, named after André-Marie Ampère.
1 Ampere = 1 Coulomb of charge flowing per second. Volt is the unit of potential difference, Coulomb is the unit of charge, and Ohm is the unit of resistance.
Which planet in our solar system has the most number of natural satellites (moons)?
Check Answer
Correct Answer: (B) Saturn
Explanation
Saturn has the most confirmed natural satellites of any planet in our solar system, surpassing Jupiter with over 140 known moons as of recent surveys.
Its largest moon, Titan, is the only moon in the solar system with a dense atmosphere.
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