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A metal crystallises in a face centred cubic structure. If the edge length of its unit cell is 'a', the closest approach between two atoms in metallic crystal will be:-

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Two stones are thrown up simultaneously from the edge of the cliff 240 m high with initial speed of 10 m/s and 40 m/s respectively. Which of the following graph best represents the time variation of relative position of the second stone with respect to the first ? (Assume stones do not rebound after hitting the ground and neglect air resistance, take $g=10m/s_{2}$) (The figure are schematic and not drawn to scale)

What is the minimum energy required to launch a satellite of mass m from the surface of a planet of mass M and radius R in a circular orbit at an altitude of 2R?

Let PS be the median of the triangle with vertices $P(2,2),Q(6,−1)andR(7,3)$. The equation of the linepassing through $(1,−1)$ and parallel to PS is

Diameter of plano-convex lens is 6 cm and thickness at the centre is 3 mm. If speed of light in material of lens is $2×10_{8}m/s,$ the focal length of the lens is :

A multiple choice examination has 5 questions. Each question has three alternative answers of which exactly one is correct. The probability that a student will get 4 or more correct answers just by guessing is

If $[a×bb×cc×a]=λ[abc]_{2}$, then l is equal to

Which of the following exists as covalent crystals in the solid state?

The ionic radii (in Å) of $N_{3−},O_{2−}$ and $F_{−}$ are respectively :