ShilpaFlame Institute

6. A liquid is kept in a cylindrical vessel which is being rotated about a vertical axis through the centre of the circular base. If the radius of the vessel is r and angular velocity of rotation is ω , then the difference in the heights of the liquid at the centre of the vessel and the edge is

(a) (rω)/(2g) (b) (r2 ω2 )/(2g) (c) √2grω (d) (ω2 /(2gr2 ) Answer-b (32)

5. A body floats in a liquid contained in a beaker. The whole system as shown falls freely under gravity. The upthrust on the body due to the liquid is

(a) Zero (b) Equal to the weight of the liquid displaced (c) Equal to the weight of the body in air (d) Equal to the weight of the immersed position of the body Answer-a (8)

18. Assertion : Machine parts are jammed in winter. Reason : The viscosity of lubricant used in machine parts increase at low temperature.

(a) If both assertion and reason are true and the reason is the correct explanation of the assertion. (b) If both assertion and reason are true but reason is not the correct explanation of the assertion. (c) If assertion is …

13. Assertion : For a floating body to be in stable equilibrium, its centre of buoyancy must be located above the centre of gravity. Reason : The torque produced by the weight of the body and the upthrust will restore body back to its normal position, after the body is disturbed.

11. Assertion : The size of the needle of a syninge controls flow rate better than the thumb pressure exerted by a doctor while administering an injection. Reason : Flow rate is independent of pressure exerted by the thumb of the doctor.

9. Assertion : The velocity of flow of a liquid is smaller when pressure is larger and viceversa. Reason : According to Bernoulli’s theorem, for the stream line flow of an ideal liquid, the total energy per unit mass remains constant.

4. A vessel contains oil

(density = 0.8 gm/cm3) over mercury (density = 13.6 gm/cm3). A homogeneous sphere floats with half of its volume immersed in mercury and the other half in oil. The density of the material of the sphere in gm/cm3 is (a) …

3. A wooden block, with a coin placed on its top, floats in water as shown in fig. the distance l and h are shown there. After some time the coin falls into the water. Then

(a) l decreases and h increases (b) l increases and h decreases (c) Both l and h increase (d) Both l and h decrease Answer-d (119)

2. A homogeneous solid cylinder of length L (L<H/2). Cross-sectional area A/5 is immersed such that it floats with its axis vertical at the liquid-liquid interface with length L/4 in the denser liquid as shown in the fig. The lower density liquid is open to atmosphere having pressure

P0 . Then density D of solid is given by (a) 5d/4 (b) 4d/5 (c) d (d) d/5 Answer-a (7)

1. A U-tube in which the cross-sectional area of the limb on the left is one quarter, the limb on the right contains mercury

(density 13.6 g/cm3). The level of mercury in the narrow limb is at a distance of 36 cm from the upper end of the tube. What will be the rise in the level of mercury in the right limb if …

28. Assertion : Bernoulli’s theorem holds for incompressible, non-viscous fluids.

Reason : The factor v2/2g is called velocity head. (a) If both assertion and reason are true and the reason is the correct explanation of the assertion. (b) If both assertion and reason are true but reason is not …

27. Assertion : Cars and aeroplanes are streamlined. Reason : This is done to reduce the backward drag due to atmosphere.

26. Assertion : When two boats sails parallel in the same direction and close to each other, they are pulled towards each other. Reason : The viscous drag on a spherical body moving with speed v is proportional to v.

20. Assertion : A rain drop after falling through some height attains a constant velocity. Reason : At constant velocity, the viscous drag is just equal to its weight.

17. Assertion : Sudden fall of pressure at a place indicates strom. Reason : Air flows from higher pressure to lower pressure.

16. Assertion : Aeroplanes are made to run on the runway before take off, so that they acquire the necessary lift. Reason : According to Bernoulli’s theorem, as velocity increases pressure decreases and viceversa.

14. Assertion : Water flows faster than honey. Reason : The coefficient of viscosity of water is less than honey.

12. Assertion : A fluid flowing out of a small hole in a vessel apply a backward thrust on the vessel. Reason : According to equation of continuity, the product of area and velocity remain constant.

10. Assertion : The shape of an automobile is so designed that its front resembles the stream line pattern of the fluid through which it moves. Reason : The resistance offered by the fluid is maximum.

8. Assertion : The velocity of fall of a man jumping with a parachute first increases and then becomes constant. Reason : The constant velocity of fall of man is called terminal velocity.

6. Assertion : A piece of ice floats in water, the level of water remains unchanged when the ice melts completely. Reason : According to Archimede’s principle, the loss in weight of the body in the liquid is equal to the weight of the liquid displaced by the immersed part of the body.

5. Assertion : A man sitting in a boat which is floating on a pond. If the man drinks some water from the pond, the level of the water in the pond decreases. Reason : According to Archimede’s principle the weight displaced by body is equal to the weight of the body.

4. Assertion : To float, a body must displace liquid whose weight is greater than the actual weight of the body. Reason : The body will experiences no net downward force, in the case of floating.

3. Assertion : Hydrostatic pressure is a vector quantity. Reason : Pressure is force divided by area, and force is a vector quantity.

2. Assertion : The blood pressure in humans is greater at the feet than at the brain. Reason : Pressure of liquid at any point is proportional to height, density of liquid and acceleration due to gravity.

1. Assertion : Pascal law is the working principle of a hydraulic lift. Reason : Pressure is equal to thrust per area.

5. From amongst the following curves, which one shows the variation of the velocity v with time t for a small sized spherical body falling vertically in a long column of a viscous liquid

Answer-d (73)

66. An incompressible fluid flows steadily through a cylindrical pipe which has radius 2r at point A and radius r at B further along the flow direction. If the velocity at point A is v, its velocity at point B is

(a) 2v (b) v (c) v/2 (d) 4v Answer-d (5)

25. Assertion : Terminal velocity is same as the critical velocity. Reason : The constant velocity of fall of a body through a viscous fluid is called terminal velocity.

24. Assertion : To empty an oil tank, two holes are made. Reason : Oil will come out two holes so it will emptied faster.

23. Assertion : It is difficult to stop bleeding from a cut in the body at high altitudes. Reason : The atmospheric pressure at high altitude is lesser than the blood pressure.

22. Assertion : Railways tracks are laid on small sized wooden sleepers. Reason : Small sized wooden sleepers are used so that rails exert more pressure on the railway track. Due to which rail does not leave the track

21. Assertion : paper pins are made to have pointed end. Reason : Because pointed pins have very smalll area due to which even for small applied force it exert large pressure on the surface.

19. Assertion : A block of wood is floating in a tank containing water. The apparent weight of the floating block is equal to zero. Reason : Because the entire weight of the block is supported by the buoyant force (the upward thrust) due to water.

15. Assertion : The viscosity of liquid increases rapidly with rise of temperature. Reason : Viscosity of a liquid is the property of the liquid by virtue of which it opposes the relative motion amongst its different layers.

7. Assertion : The velocity increases, when water flowing in broader pipe enter a narrow pipe. Reason : According to equation of continuity, product of area and velocity is constant.

4. Water flows through a frictionless duct with a cross-section varying as shown in fig. Pressure p at points along the axis is represented by

Explanation-(a) When cross-section of duct is decreased, the velocity of water increased and in accordance with Bernoulli’s theorem, the pressure P decreased at that place. (47)