9th SA-2 Solved Practice paper [Physics and Chemistry] 2014

     9^th SA-2 Solved Practice paper [Physics and Chemistry] 2014

1. Name the anion and cation which constitute the molecule of magnesium oxide   [1]

2. A cube of side 5cm is immersed in water and then in saturated salt solution. In which case will it experience a greater buoyant force. If each side of the cube is reduced to 4cm and then immersed in water compare the force experienced by the cube, as compared to the first case. Give reasons for each case. 2

3. The kinetic energy of an object of mass `m’ moving with a velocity of 5ms-1 is 25J. Calculate its kinetic energy when its velocity is doubled. 2

4. The percentage of three elements calcium, carbon and oxygen in a sample of calcium carbonate is given as : [3]

Calcium =40% ; Carbon =12.0% ; Oxygen = 48%

If the law of constant proportion is true, what weights of these elements will be present in 1.5 g of another sample of calcium. Carbonate ? (Atomic mass of Ca = 40 u, C = 12 u, O = 16 u)

5.  The description of atomic particles of two elements X and Y is given below[3]

X Y Protons  8  8 neutrons 8 9 electrons 8 8

(i) What is the atomic number of Y?

(ii) What is the mass number of X?

(iii) What is the relation between X and Y?

(iv) Which element/elements do they represent?

(v) Write the electronic configuration of X?

(vi) Write the cation/anion formed by the element

6. Which of the following are isotopes and which are isobars?

Argon, Protium, Calcium, Deuterium. Explain why the isotopes have similar chemical properties but they differ in physical properties? [3]

7.What do you mean by buoyancy? Why does an object float or sink when placed on the surface of water?[3]

8. When is the work done by a force said to be negative? Give one situation in which one of the forces acting on the object is doing positive work and the other is doing negative work. [3]

9. Define one Joule of work. Calculate the work done in lifting a box weighting 150 kg through a vertical height of 7 meters (take g=10 ms2) [3]

10. A construction worker’s helmet slips and falls when he is 78.4 m above the ground. He hears the sound of the helmet hitting the ground 4.23 seconds after it slipped. Find the speed of sound on air. [3]

11. Answer these questions[5]

(i) Define mole

(ii) How is it related to Avogadro constant, relative mass and molecular mass?

(iii) What is the number of molecules in 0.25 moles of oxygen ? Avogadro’s no. = 6 .22 x1023.

OR

(i) Define atomicity

(ii) Give an example each of a polyatomic element and a polyatomic ion.

(iii) How many atoms are present in CaCl2 molecule and ion? SO4-2

(iv) Write down the formulae of

(a) sodium carbonate

(b) Ammonium chloride

(c) Zinc oxide

(d) Aluminium hydroxide

12. (i) An object thrown at a certain angle to the ground moves in a curved path and falls back to the ground. The initial and the final points of the path of the object lie on the same horizontal line. What is the total work done against the force of gravity and by the force of gravity on the object? Explain with proper mathematical expressions.

(ii) Certain force acting on 20kg mass changes its velocity from 5ms-1 to 2ms-1 calculates the work done by the force. [5]

OR,

(i) Define kinetic energy. Derive an expression for the kinetic energy of an object.

(ii) The power of a motor pump is 5kW. How much water per minute the pump can raise to height of 20m? Take g=10ms-2

Solution:

1.		Magnesium oxide – MgO Anion – O-2 Cation – Mg+2		½ ½
2		We know buyant force = V.P g V = Volume of body P = density of liquid g = acceleration Since density of saturated salt solutions is more than water the cube will experience greater upthrust. In second case as volume of cube is less then first so in 2nd case it will experience less upthrust		½ ½ ½ ½
3		Initial K.E = 25J Since K.E = ½ mv2 D as velocity doubles K.S becomes 4 times K.E = 4x25=100J		1 1
4		Mass of calcium in 1.5 g of sample  = 40 x [1.5/100] = 9.6 g Mass of carbon in 1.5 g of sample = 12x [1.5/100] = 0.18 g Mass of oxygen in 1.5 g of sample = 48x[1.5/100] = 0.72 g		1 1 1
5		(i) Atomic number of y – 8 (ii) Mass number of x – 16 (iii) x and y are isotopes (iv) x and y represent – oxygen (v) 168O - 2, 6 (vi) It will form an anion – O-2		1 1 1
6		Isotopes – Protium, Diuterium Isobars – Argon and calcium Since isotopes have identical electronic configuration containing same number of valence electrons they have similar chemical properties. Since the masses are slightly different the physical properties (density, melting pt, boiling pt, etc) are different		1 1
7		When a body is immersed in a fluid, it experiences an upward force. This upward force is the force of buoyancy. Forces acting an the body inside water are buoyant force weight of body and if the buoyant force is greater than the gravitational force it floats, otherwise it sinks.		1 2
8		Negative work – When the force is acting opposite to the direction of the displacement, the work done by the force is taken as negative. When we lift an object two forces act on the object. Muscular force – Doing positive work in the direction of the displacement. Gravitational force – doing negative work opposite to the direction of the displacement.		1 1 1
9		One Joule is the amount of work done on an object when a force of 1N displaces it by 1 m along the line of action of force  m = 150kg  ; G = 10m/s2  ;   h = 7m P.E = mgh P.E = 150 x 10 x7 = 10500J		1 2
10		We know, h = ut + 1/2 gt2 u = 0, h = 78.4, g = 9.8 m/s2 using these t2 = 16 Þ t =  4 s time taken by the helmet reach the ground = 4 s Þ time taken by sound to reach the height = 4.23 – 4 = 0.23s ÞSpeed of sound =  78.4 /0.23 = 340.87 m/s		1 1 1
11		(i) Mole – one mole of any species (atoms, molecules, ions or particles) is that quantity in number having a mass equal to its atomic or molecular mass in grams (ii) 1 mole = 6.022 x 1023 in number – Relative mass in g. (iii) 1 mole of oxygen contain 6.022 x 1023 molecules 0.25 mole of oxygen contain 6.022 x1023 x 0.25 = 1.505 x 1023 molecules		1 2 2
OR		(i) Atomicity – Number of atoms constituting a molecule (ii) Polyatomic element – sulphur Polyatomic ion – NH4-, OH-, SO4-2 (any one) (iii) Cacl2 – atomicity – 3 SO4-2 – atomicity - 5 (iv) (a) Na2CO3 Sodium carbonate (b) NH4Cl Ammonium chloride (c) ZnO zinc oxide (d) Al(OH)3 Aluminium hydroxide	1 ½+½ ½+½ ½+½+ ½+½
12.		(i) Work done = mgh Difference in height of initial and final position is zero. Work done = mg ( h2 - h1)                     =  mg(o) = O (ii) Work done =  change in K.E Work done  = 1/2 m (v12 – v22) = ½ x 20(52  - 22) = 210 J		1 ½ 1 1 ½
OR
(i) Energy posesed by a body by virtue of motion. F = ma W = F.S = mas But u2 - v2 = 2as Þ as =  ½ (v2-u2) w = energy Þ S = v2/2a m. a x x v2 x 2a = 1/2mv2				½ ½ ½ ½
(ii) Energy = power x time =  5kw x 1 min = 3 x 105 J mgh = E /gh  = (3 x 105)/ 10x 20 =  1.5 x 103 kg volume of water  =  mass/ density = (1.5 x 103 )/103 = 1.5 m3				½ ½ 1
13	(i)
(ii)	Eardrum moves inwards when compression reaches it and moves outwards when rarefaction reaches it thus the ear drum vibrates. (ii) Audible rang 20Hz to 20,000 Hz OR
(i)	Ceiling and walls are made curved so that sound after reflection reaches the target audience. (ii) Reflection The sound goes to the obstacle and reaches back the ear of the listeners on reflection after 0.1s. If speed of sound in air is 344 m/s then the minimum distance of obstacle from the source of sound must be 17.2 cm (iii) Repeated reflection of sound that results in persistence of sound- Reverberation. sound is blurred, distorted, confusing sound absorbent material on roof, walls, seats

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