2018-10-01_Physics_For_You

10. When the tension in a metal wire is T 1 , its length is
    l 1. When the tension is T 2 , its length is l 2. Find the
    natural length of wire.


11. Why does modulus of elasticity of most of
    the materials decrease with the increase of
    temperature?
    OR
    If n identical water droplets falling under gravity
    with terminal velocity v coalesce to form a single
    drop which has the terminal velocity 4v, nd the
    number n.


12. A bubble having surface
    tension S and radius R is
    formed on a ring of radius b
    (b<<R). Air is blown inside
    the tube with velocity v as
    shown in gure. e air molecule collides
    perpendicularly with the wall of the bubble and
    stops. Calculate the radius at which the bubble
    separates from the ring.
    SECTION C


13. A square lead slab of side 50 cm and thickness
    10 cm is subjected to a shearing force (on its narrow
    face) of 9.0 × 10^4 N. e lower edge is riveted to the
    oor. How much will the upper edge be displaced?
    If modulus of rigidity (G) is 5.6 × 10^9 N m–2.


14. State and prove Torricelli's theorem.


15. (i) A ball oats on the surface of water in a
    container exposed to the atmosphere. Will the
    ball remain immersed at its initial depth or
    will it sink or rise somewhat if the container is
    shied to the moon?
    (ii) e viscous force ‘F’ acting on a body of radius
    ‘r’ moving with a velocity ‘v’ in a medium
    of coecient of viscosity ‘K’ is given by
    F = 6pKrv. Check the correctness of the
    formula.


16. Stress strain curve for two wires of material
    A and B are as shown in gure.

Stress

Strain

wireB

wireA

(a) Which material is more ductile?
(b) Which material has greater value of Young's
modulus?

(c) Which of the two is stronger material?

(d) Which material is more brittle?

17. Explain why
    (i) a balloon lled with helium does not rise in
    air indenitely but halts aer a certain height
    (Neglect winds)?
    (ii) the force required by a man to raise his limbs
    immersed in water is smaller than the force
    for the same movement in air?


18. Water from a tap emerges vertically downwards
    with an initial velocity v 0. Assume pressure is
    constant throughout the stream of water and the
    ow is steady, nd the distance from the tap at
    which cross-sectional area of stream is half of the
    cross-sectional area of stream at the tap.


19. A cable is replaced by another cable of the same
    length and material but of twice the diameter.
    (a) How does this aect its elongation under a
    given load?
    (b) How many times will be the maximum load it
    can now support without exceeding the elastic
    limit?


20. (i) For the area of the hole
    is much lesser than the
    area of the base of a vessel
    of liquid, nd velocity of
    eux v of the liquid if
    vessel is accelerating as
    shown in gure.
    (a 0 = vertical acceleration)
    (ii) A large open tank has two holes in the wall.
    One is a square hole of side L at a depth y
    from the top and the other is a circular hole
    of radius R at a depth 4y from the top. When
    the tank is completely lled with water, the
    quantities of water owing out per second
    from both holes are the same. en, what is
    the value of R?

MONTHLY TUNE UP CLASS XI ANSWER KEY

1. (a) 2. (b) 3. (a) 4. (a) 5. (d)


2. (b) 7. (b) 8. (b) 9. (d) 10. (c)


3. (b) 12. (a) 13. (a) 14. (d) 15. (c)


4. (a) 17. (b) 18. (a) 19. (c) 20. (a, b, c)


5. (a, b, c, d) 22. (b, d) 23. (a, b, c)


6. (4) 25. (123) 26. (2) 27. (d) 28. (b)


7. (a) 30. (c)