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Question

If the radius of a right circular cone cone is increased by 50%. its volume increases by

The correct answer is
125%

Volume Calculation for a Right Circular Cone

The volume ($V$) of a right circular cone is given by the formula:

$ V = \frac{1}{3} \pi r^2 h $

where $r$ is the radius of the base and $h$ is the height of the cone.

Calculating Initial Volume

Let the initial radius be $r$ and the initial height be $h$. The initial volume ($V_1$) is:

$ V_1 = \frac{1}{3} \pi r^2 h $

Calculating New Volume After Radius Increase

The radius is increased by 50%. The new radius ($r'$) is:

  • Increase in radius = $50\%$ of $r = 0.50r$.
  • New radius, $r' = r + 0.50r = 1.5r$.

The height ($h$) remains unchanged. The new volume ($V_2$) is:

$ V_2 = \frac{1}{3} \pi (r')^2 h $

Substitute $r' = 1.5r$:

$ V_2 = \frac{1}{3} \pi (1.5r)^2 h $

$ V_2 = \frac{1}{3} \pi (2.25 r^2) h $

$ V_2 = 2.25 \times \left( \frac{1}{3} \pi r^2 h \right) $

Since $V_1 = \frac{1}{3} \pi r^2 h$, we have:

$ V_2 = 2.25 V_1 $

Determining Percentage Volume Increase

The increase in volume is:

$ \Delta V = V_2 - V_1 = 2.25 V_1 - V_1 = 1.25 V_1 $

The percentage increase in volume is calculated as:

$ \text{Percentage Increase} = \frac{\Delta V}{V_1} \times 100\% $

$ \text{Percentage Increase} = \frac{1.25 V_1}{V_1} \times 100\% $

$ \text{Percentage Increase} = 1.25 \times 100\% = 125\% $

Therefore, if the radius of a right circular cone is increased by 50%, its volume increases by 125%.

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Important Questions from Mensuration and Geometry

  1. In the given figure, PQRS is a square of side 2 cm and PLMN is a rectangle. The corner L of the rectangle is on the side QR. Side MN of the rectangle passes through the corner S of the square.
    What is the area (in cm²) of the rectangle PLMN?
    Note: The figure shown is representative.

  2. A regular dodecagon (12-sided regular polygon) is inscribed in a circle of radius $r$ cm as shown in the figure. The side of the dodecagon is $d$ cm. All the triangles (numbered 1 to 12) in the figure are used to form squares of side $r$ cm and each numbered triangle is used only once to form a square.
    The number of squares that can be formed and the number of triangles required to form each square, respectively, are:
    Note: The figure shown is representative.

  3. Which one of the following options has the correct sequence of objects arranged in the increasing number of mirror lines (lines of symmetry)?
  4. A circle with center at $(x, y) = (0.5, 0)$ and radius $= 0.5$ intersects with another circle with center at $(x, y) = (1, 1)$ and radius $= 1$ at two points. One of the points of intersection $(x, y)$ is:
  5. During a half-moon phase, the Earth-Moon-Sun form a right triangle. If the Moon-Earth-Sun angle at this half-moon phase is measured to be $89.85^{\circ}$, the ratio of the Earth-Sun and Earth-Moon distances is closest to
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