Explain why
(a) To keep a piece of paper horizontal, you should blow over, not under, it
(b) When we try to close a water tap with our fingers, fast jets of water gush
through the openings between our fingers
(c) The size of the needle of a syringe controls flow rate better than the thumb
pressure exerted by a doctor while administering an injection
(d) A fluid flowing out of a small hole in a vessel results in a backward thrust on
the vessel
Fill in the blanks using the word from the list appended with each statement:
(a) Surface tension of liquids generally … with temperatures (increases / decreases)
(b) Viscosity of gases … with temperature, whereas viscosity of liquids … with
temperature (increases / decreases)
(c) For solids with elastic modulus of rigidity, the shearing force is proportional
to … , while for fluids it is proportional to … (shear strain / rate of shear
strain)
(d) For a fluid in a steady flow, the increase in flow speed at a constriction follows
(conservation of mass / Bernoulli’s principle)
(e) For the model of a plane in a wind tunnel, turbulence occurs at a … speed for
turbulence for an actual plane (greater / smaller)
Explain why
(a) The angle of contact of mercury with glass is obtuse, while that of water with glass is acute.
(b) Water on a clean glass surface tends to spread out while mercury on the
same surface tends to form drops. (Put differently, water wets glass while
mercury does not.)
(c) Surface tension of a liquid is independent of the area of the surface
(d) Water with detergent disolved in it should have small angles of contact.
(e) A drop of liquid under no external forces is always spherical in shape
Explain why
(a) The blood pressure in humans is greater at the feet than at the brain
(b) Atmospheric pressure at a height of about 6 km decreases to nearly half of
its value at the sea level, though the height of the atmosphere is more than
100 km
(c) Hydrostatic pressure is a scalar quantity even though pressure is force
divided by area.
The average depth of Indian Ocean is about 3000 m. Calculate the fractional compression, ∆V/V, of water at the bottom of the ocean, given that the bulk modulus of water is 2.2 × 10⁹ N m–2. (Take g = 10 m s–2)
A square lead slab of side 50cm and thickness 10 cm is subject to ashearing force (on its narrow face) of 9.0 ×10⁴N. The lower edge is riveted to the floor. How much will the upper edge be displaced?
In a human pyramid in a circus, the entire weight of the balanced group is supported by the legs of a performer who is lying on his back (as shown in Fig. 9.5). The combined mass of all the persons performing the act, and the tables, plaques etc. involved is 280 kg. The mass of the performer lying on his back at the bottom of the pyramid is 60 kg. Each thighbone (femur) of this performer has a length of 50 cm and an effective radius of2.0 cm. Determine the amount by which each thighbone gets compressed under theextra load.
A copper wire of length 2.2m and a steel wire of length 1.6 m, both of diameter 3.0 mm, are connected end to end.When stretched by a load, the netelongation is found to be 0.70 mm. Obtainthe load applied.
A structural steel rod has aradius of 10 mm and a length of 1.0 m. A100 kN force stretches it along its length.Calculate
(a) stress,
(b) elongation, and
(c)
strain on the rod. Young’s modulus, of structural steel is 2.0 × 10¹¹ N m-².
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