Question : A well with an inner radius of 3 m, is dug 6 m deep. The soil taken out of it has been spread evenly all around it to a width of 2 m to form an embankment. The height (in m) of the embankment is:
Option 1: $4 \frac{1}{2}$
Option 2: $4 \frac{1}{4}$
Option 3: $3 \frac{1}{4}$
Option 4: $3 \frac{3}{8}$
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Correct Answer: $3 \frac{3}{8}$
Solution : The volume of the well (a cylinder) is $\pi r^2 h$, where $r$ is the radius and $h$ is the height. Substituting r = 3 m and h = 6 m. The volume of the well = $\pi r^2 h= \pi \times 3^2 \times 6 =54\pi \;m^3$ The embankment is in the shape of a hollow cylinder with an outer radius, R = r + width = 3 + 2 = 5 m and an inner radius r = 3 m. Let the height of the embankment be $h_2$. The volume of the embankment = $\pi (R^2 - r^2) h_2$ Equating the volume of the well and the embankment, $⇒54\pi = \pi (5^2 - 3^2) h_2$ Solving for $h_2$, $⇒h_2 = \frac{54}{16} = \frac{27}{8} = 3\frac{3}{8}\;m$ Hence, the correct answer is $3\frac{3}{8}$.
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Question : A well of 3 m in diameter is dug 14 m deep. The earth taken out of it has been spread evenly all around it in the shape of a circular ring of width 4 m to form an embankment. Find the height of the embankment.
Option 1: 4.25 m
Option 2: 2.25 m
Option 3: 1.125 m
Option 4: 1.75 m
Question : A ball is to be made with an inner radius of 2 units and an outside radius of 3 units. How much material is required to make the ball?
Option 1: $\frac{19}{3} \pi$
Option 2: $19 \pi$
Option 3: $\frac{76}{3} \pi$
Option 4: $\pi$
Question : An athlete runs 8 times around a circular field of radius 7 m in 3 minutes 40 seconds. His speed (in km/hr) is: (Take $\pi=\frac{22}{7}$ )
Option 1: $\frac{72}{25}$
Option 2: $\frac{118}{25}$
Option 3: $\frac{144}{25}$
Option 4: $\frac{108}{25}$
Question : The radius of the incircle of an equilateral $\Delta$ ABC of side $2\sqrt{3}$ cm is $x$ cm. The value of $x$ is:
Option 1: $\frac{1}{3}$
Option 2: $\frac{1}{2}$
Option 3: $1$
Option 4: $\sqrt{3}$
Question : If $\tan A = n\tan B$ and $\sin A=m \sin B$, then the value of $\cos^{2}A$ is:
Option 1: $\frac{m^{2}-1}{n^{2}+1}$
Option 2: $\frac{m^{2}+1}{n^{2}-1}$
Option 3: $\frac{m^{2}+1}{n^{2}+1}$
Option 4: $\frac{m^{2}-1}{n^{2}-1}$
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