Question Detail
The perimeter of one face of a cube is 20 cm. Its volume will be:
- \begin{aligned} 125 cm^3 \end{aligned}
- \begin{aligned} 400 cm^3 \end{aligned}
- \begin{aligned} 250 cm^3 \end{aligned}
- \begin{aligned} 625 cm^3 \end{aligned}
Answer: Option A
Explanation:
Edge of cude = 20/4 = 5 cm
Volume = a*a*a = 5*5*5 = 125 cm cube
1. The volume of the largest right circular cone that can be cut out of a cube of edge 7 cm is:
- \begin{aligned} 79.8 cm^3 \end{aligned}
- \begin{aligned} 79.4 cm^3 \end{aligned}
- \begin{aligned} 89.8 cm^3 \end{aligned}
- \begin{aligned} 89.4 cm^3 \end{aligned}
Answer: Option C
Explanation:
Volume of the largest cone = Volume of the cone with diameter of base 7 and height 7 cm
\begin{aligned}
\text{Volume of cone =}\frac{1}{3}\pi r^2h \\
= \frac{1}{3}*\frac{22}{7}*3.5*3.5*7 \\
= \frac{269.5}{3}cm^3 \\
= 89.8 cm^3
\end{aligned}
Note: radius is taken as 3.5, as diameter is 7 cm
2. A hemisphere and a cone have equal bases. If their heights are also equal, then the ratio of their curved surface will be :
- \begin{aligned} 2:1 \end{aligned}
- \begin{aligned} 1:\sqrt{2} \end{aligned}
- \begin{aligned} \sqrt{2}:1 \end{aligned}
- \begin{aligned} \sqrt{3}:1 \end{aligned}
Answer: Option C
Explanation:
Let the radius of hemisphere and cone be R,
Height of hemisphere H = R.
So the height of the cone = height of the hemisphere = R
Slant height of the cone
\begin{aligned}
= \sqrt{R^2+R^2} \\
= \sqrt{2}R \\
\frac{\text{Hemisphere Curved surface area}}{\text{Cone Curved surface area}} = \\
\frac{2\pi R^2}{\pi *R*\sqrt{2}R} \\
= \sqrt{2}:1
\end{aligned}
3. 12 spheres of the same size are made from melting a solid cylinder of 16 cm diameter and 2 cm height. Find the diameter of each sphere.
- 4 cm
- 6 cm
- 8 cm
- 10 cm
Answer: Option A
Explanation:
In this type of question, just equate the two volumes to get the answer as,
\begin{aligned}
\text{Volume of cylinder =}\pi r^2h\\
\text{Volume of sphere =} \frac{4}{3}\pi r^3\\
=> 12*\frac{4}{3}\pi r^3 = \pi r^2h \\
=> 12*\frac{4}{3}\pi r^3 = \pi *8*8*2 \\
=> r^3 = \frac{8*8*2*3}{12*4} \\
=> r^3 = 8 \\
=> r = 2 cm \\
=> \text{Diameter =}2*2 = 4 cm
\end{aligned}
4. A hollow spherical metallic ball has an external diameter 6 cm and is 1/2 cm thick. The volume of metal used in the metal is:
- \begin{aligned} 47\frac{1}{5} cm^3 \end{aligned}
- \begin{aligned} 47\frac{3}{5} cm^3 \end{aligned}
- \begin{aligned} 47\frac{7}{5} cm^3 \end{aligned}
- \begin{aligned} 47\frac{9}{5} cm^3 \end{aligned}
Answer: Option B
Explanation:
Please note we are talking about "Hollow" ball. Do not ignore this word in this type of question in a hurry to solve this question.
If we are given with external radius and thickness, we can get the internal radius by subtracting them. Then the volume of metal can be obtained by its formula as,
External radius = 3 cm,
Internal radius = (3-0.5) cm = 2.5 cm
\begin{aligned}
\text{Volume of sphere =}\frac{4}{3}\pi r^3 \\
= \frac{4}{3}*\frac{22}{7}*[3^2 - 2.5^2]cm^3 \\
= \frac{4}{3}*\frac{22}{7}*\frac{91}{8}cm^3 \\
= \frac{143}{3} cm^3 \\
= 47\frac{2}{3}cm^3
\end{aligned}
5. Find the surface area of a 10cm*4cm*3cm brick.
- 154 cm square
- 156 cm square
- 160 cm square
- 164 cm square
Answer: Option D
Explanation:
Surface area of a cuboid = 2(lb+bh+hl) cm square
So,
Surface area of a brick = 2(10*4+4*3+3*10) cm square
= 2(82) cm square = 164 cm square