Why do twentieth century advances not seem sustainable?
Check Answer
Correct Answer: (B) Due to the increased cost of agricultural production
Explanation
What pushes farmers into places unsuited for agriculture?
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Correct Answer: (A) Population growth
Explanation
Which one of the following is NOT true, according to the passage, for ecological degradation?
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Correct Answer: (D) World War II
Explanation
What is the conclusion of the author in the passage about the prospects of agriculture in the world?
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Correct Answer: (A) The author is both hopeful and sceptical of the prospects of agriculture
Explanation
Which one of the following words means 'incursion'?
Check Answer
Correct Answer: (A) invasion
Explanation
Convert from direct into indirect speech. Ayushi said to the group, "We have had enough of suffering today. It is time to march forward."
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Correct Answer: (A) Ayushi told the group that they had had enough of suffering that day and it was time to march forward
Explanation
Convert from direct speech into indirect speech. "Alas! We lost the match by one point," said the Captain
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Correct Answer: (A) The Captain regretted that they had lost the match by one point
Explanation
Convert from direct speech into indirect speech. "Where were you last week?" Alok asked Sheela
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Correct Answer: (B) Alok asked Sheela where she had been the week before
Explanation
The king who the people loved built the castle five centuries ago
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Correct Answer: (A) The castle was built five centuries ago by the king who was loved by the people
Explanation
The company has recruited four hundred engineers who will have to complete an internship for three weeks
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Correct Answer: (A) Four hundred engineers have been recruited by the company and an internship of three weeks will have to be completed by them
Explanation
A biconvex lens is formed by using two thin planoconvex lenses, as shown in the figure. The refractive index and radius of curved surfaces are also mentioned in figure. When an object is placed on the left side of lens at a distance of $30$ cm from the biconvex lens, the magnification of the image will be: | Image: Q35
Check Answer
Correct Answer: (D) -2
Explanation
Assuming the standard parameters for the two identical planoconvex lenses given in the figure are refractive index $n = 1.5$ and radius of curvature $R = 20 \text{ cm}$.
The focal length of each planoconvex lens is:
$$ f_1 = \frac{R}{n - 1} = \frac{20}{1.5 - 1} = \frac{20}{0.5} = 40 \text{ cm} $$
When two such lenses are combined to form a biconvex lens, the equivalent focal length $f$ is:
$$ \frac{1}{f} = \frac{1}{f_1} + \frac{1}{f_2} = \frac{1}{40} + \frac{1}{40} = \frac{2}{40} \implies f = 20 \text{ cm} $$
Given the object distance $u = -30 \text{ cm}$, we use the lens formula to find the image distance $v$:
$$ \frac{1}{v} - \frac{1}{u} = \frac{1}{f} \implies \frac{1}{v} - \frac{1}{-30} = \frac{1}{20} $$
$$ \frac{1}{v} = \frac{1}{20} - \frac{1}{30} = \frac{3 - 2}{60} = \frac{1}{60} \implies v = 60 \text{ cm} $$
The magnification $m$ of the image is:
$$ m = \frac{v}{u} = \frac{60}{-30} = -2 $$
A small block of mass $m$ slides down from the top of a frictionless inclined surface, while the inclined plane is moving towards left with constant acceleration $a_0$. The angle between the inclined plane and ground is $\theta$ and its base length is $L$. Assuming that initially the small block is at the top of the inclined plane, the time it takes to reach the lowest point of the inclined plane is _______. [NEED TO ADD IMAGE]
Check Answer
Correct Answer: (A) \sqrt{\frac{4L}{g \sin 2\theta - a_0 (1 + \cos 2\theta)}}
Explanation
Let's analyze the motion of the block relative to the inclined plane. The incline is moving to the left with an acceleration $a_0$.
In the reference frame of the inclined plane, a pseudo force $ma_0$ acts on the block towards the right.
The block slides down the incline (which implies moving towards the left horizontally). The components of forces along the incline (downwards) are:
1. Component of gravity: $mg \sin \theta$
2. Component of pseudo force (acting up the incline): $-ma_0 \cos \theta$
The net acceleration of the block relative to the incline is:
$$ a_{rel} = g \sin \theta - a_0 \cos \theta $$
The distance the block needs to travel along the incline is $s = \frac{L}{\cos \theta}$.
Using the second equation of motion $s = \frac{1}{2} a_{rel} t^2$:
$$ \frac{L}{\cos \theta} = \frac{1}{2} (g \sin \theta - a_0 \cos \theta) t^2 $$
$$ t^2 = \frac{2L}{\cos \theta (g \sin \theta - a_0 \cos \theta)} = \frac{2L}{g \sin \theta \cos \theta - a_0 \cos^2 \theta} $$
Using trigonometric identities $\sin 2\theta = 2 \sin \theta \cos \theta$ and $1 + \cos 2\theta = 2 \cos^2 \theta$:
$$ t^2 = \frac{4L}{2g \sin \theta \cos \theta - 2a_0 \cos^2 \theta} = \frac{4L}{g \sin 2\theta - a_0 (1 + \cos 2\theta)} $$
$$ t = \sqrt{\frac{4L}{g \sin 2\theta - a_0 (1 + \cos 2\theta)}} $$
A thermodynamic system is taken through the cyclic process ABC as shown in the figure. The total work done by the system during the cycle ABC is ______ J. [NEED TO ADD IMAGE]
Check Answer
Correct Numerical Answer: 0
Explanation
The problem refers to a figure showing the cyclic process ABC, which is missing from the provided text. The total work done by the system during a cyclic process is equal to the area enclosed by the cycle on a P-V diagram. Without the coordinates of the points A, B, and C, the exact numerical value cannot be determined. (Placeholder answer provided).
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