Physics May/June 2010

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Question 1
A stone is projected vertically upward with a speed of 30 ms” from the top of a tower of height 50 m. Neglecting air resistance, determine the maximum height it reached from the ground [g = 10 ms²]

ANSWER

v2 =u2 – 2gx
At maximum height v = 0
o = 302 – 2 x lOx
o = 900 – 20 x
x = 45m.
Height from ground = 50 + 45
= 95m

Question 2
A force of 40 N is applied at the free end of a wire fixed at one end to produce an extension of 0.24 nun. if the original length and diameter of the wire are 3 m and 2.0 nun respectively, calculate the: (a) stress on the wire; (b) strain in the wire.

ANSWER

(a)        Stress = Force = F
                            Area   A

          =        40
3.14 (1.0 X 10-3)2
= 1.27 X 10-7 Nm-2
(b)       Strain = Extemion or      e
                           Length                l
= 0.24 X 10-3
3
= 8.0 X 10-5

Question 3
When a lead-acid accumulator is fully charged, evolution of gases occurs at the electrodes. Name these gases and the respective electrodes at which they are given off.

ANSWER

The gases are :
(i) Hydrogen
(ii) Oxygen
The electrodes at which they are evolved:
(i) Hydrogen Anode/lead peroxide
(ii) Oxygen Cathode/lead plate

(a) State two factors which affect the mass of elements deposited during electrolysis. (b) List two non-electrolytes.
___________________________

ANSWER

(a)Any two correct factors
e.g
time
current/quantity of charge
nature/e.c.e of element.
(b)Any two correct non-electrolytes
e.g
water
kerosene
petrol
benzene
ethanol

Question 5
(a) Differentiate between plane polarization and interference as applied to waves. (b) List two uses of polaroids.

ANSWER

(a) Any 2 correct pair
e.g.

(b) Any two correct uses of polaroids 2 x 1/2 mark
e.g They are used in:
production of 3-dimentional films
determination of concentration of sugar solution
polaroid cameras
sun glasses.

Question 6

(a) List two examples each of substances with:
(i) low viscosity;
(ii) high viscosity.
(b) When is a liquid said to be viscostatic?

ANSWER

(a) (i) Any two correct examples
e.g.
water
kerosene
ethanol
methylated spirits.
(ii) Any correct two examples
e.g.
palm oil
engine oil
glycerine
(b) A liquid is visco static if of its viscosity does not change (appreciably) with change in temperature.

Question 7

State one reason each why cathode rays:
(a)are not electromagnetic waves;
(b)cast sharp shadows of objects in their path;
(c) can rotate a light paddle wheel inside a discharge tube

ANSWER

Because they
(a) are deflected by electric and/or magnetic field(s)
(b)travel in straight paths (rectilinear propagation)
(c)posses momentum

Question 8

An X-ray tube operates at a potential of2500 V. lfthe power of the tube is 750 W, calculate the
speed of the electron striking the target.
[ e = 1.6 x 10-19 C; mass of electron = 9.1 x 10-31 kg]

ANSWER

eV = 1/2mv²
1.6 x 10-19 x 2500 = Yz x 9.1 X 10-31 x v²
v² = 8.79 X 1014
V = 2.96 X 107 ms²;

Question 9

(a) Write down the names of two particles used in explaining the wave nature of matter
(b)State the wave characteristics which are exhibited by the particles named in (a) above.

ANSWER

(a) Any correct 2
e.g.
Electron
Hydrogen atom/proton
Helium atom
Helium nucleus/alpha particle
Neutron
(b)Wave characteristics exhibited are:
diffraction
interference

Question 10

(a)State the Heisenberg Uncertainty Principle.
(b)The product of the uncertainties in Heisenberg Uncertainty Principle is equal to or greater than a constant. State the mathematical expression for this constant.

ANSWER

a) It is impossible to determine (accurately) both the wave properties of matter and its particulate properties at the same time OR In any simultaneous determination of the position x and momentum p of a particle, there.
is an uncertainty in its position L\ x and an uncertainty in its momentum ∆p.
(b) 1) ORh
2π

Question 11

(a) Distinguish between perfectly elastic collision and perfectly inelastic collision.
(b)Sketch a distance – time graph for a particle moving in a straight line with:
(i) uniform speed;
(ii) variable speed
(c)A body starts from rest and travels distances of 120,300 and 180 m in successive equal time intervals of 12 s. During each interval the body is uniformly accelerated.
(i)Calculate the velocity of the body at the end of each successive time interval
(ii)Sketch a velocity-time graph for the motion.

ANSWER

(a)Any 2 correct pairs

(c)(i) 1st stage of motion

x = ut + 1/2at²
120 = 0 x 12 + 1/2 X a x 12²
a= 5/3
V₁ = 5/3 x 12 = 20 ms^-1

2nd stage of motion
x = ut + 1/2at²
300 =, 20 x 12 + ½ x a x 12²
60 = 72a
a = 5/6

V = 5/6 x 12 = 10

V₂= 10 + 20
= 30ms·¹

3rd stage of motion

x = ut + 1/2at²
180 == 30 x 12 + ½ x a x 12²
180 = 72 a
a = – 5/2
V = -5/2 x 12= -30
V3 = 30 + -30
= 0 ms·¹

(ii)

Correct shape of each segment in relation to axes
Origin, (0.0) labeled
Only one axis labeled

Question 12
(a)Explain the terms: (i) Inertia; (ii) Inertia mass. (b)List three factors which affect the rate of evaporation of water in a pond. (c)Two ice cubes pressed together for some time were found to stick together when the pressure was removed. Explain this observation (d)Two vertical capillary tubes of the same diameter are lowered into beakers situated at the same level containing liquids A and B of densities 9.2 x 10² kgm -3 and 1.30 x 10³ kgm-3respectively. A suction pump is used to withdraw air from the top of the liquid columns in the tubes by means of aT-piece arrangement until the liquid in a rises to a height of26.0 ern. Calculate the height of the liquid in tube B.

Question 12

(a)Explain the terms:
(i) Inertia;
(ii) Inertia mass.
(b)List three factors which affect the rate of evaporation of water in a pond.
(c)Two ice cubes pressed together for some time were found to stick together when the pressure was removed. Explain this observation
(d)Two vertical capillary tubes of the same diameter are lowered into beakers situated at the same level containing liquids A and B of densities 9.2 x 10² kgm -3 and 1.30 x 10³ kgm-3respectively. A suction pump is used to withdraw air from the top of the liquid columns in the tubes by means of aT-piece arrangement until the liquid in a rises to a height of26.0 ern. Calculate the height of the liquid in tube B.

ANSWER

(a)(i)Inertia is the reluctance of a body to move if it is at rest or to stop if it is already in motion. The more mass a body has the greater its inertia.
(ii) Inertial mass represents resistance to any type of force whatever the more mass a body has the more force that is required to give it an acceleration. the mass of anobject appearing in the expression
Force = mass x acceleration is the inertial mass

(b)Any 3 correct factors
e.g
temperature
pressure
wind
area exposed
humidity/dryness of the air
( c) Ice melts if ( sufficient) pressure is applied to it. This is because an increase in pressure lowers the melting point of ice. When the two ice cubes are pressed together, melting point of ice is lowered, so they melt to form a thin layer of water (between them). On releasing the pressure, the water formed freezes because decrease in pressure raises the freezing point. Hence the two cubes stick together.
(d)P =pgh
h_AP_A = h_B P_B
26xO.92x 10³ =hBx 1.30 x 10³
hB = 26xO.92x 10³
1.30 x 10³
= 18.4 cm

Question 13

(a) State two factors which affect the angle of deviation of a ray of light through a triangular glass prism.
(b)Seven virtual images of an object are formed when two plane mirrors are inclined at an angle 0 to each other. Calculate the value of 0
(c)By means of a ripple tank, a student was able to generate series of transverse waves by varying the frequency ofthe dipper and all the waves so generated covered a distance of 0.80 m in 0.2 s.
(i)Determine the speed, v, of the waves
(ii)Copy and complete the table given above in your answer booklet.
(iii)Plot a graph with f on the vertical axis and h^-1 on the horizontal axis.
(iv)What does the slope of the graph represent?

f(Hz)	λ/m	λ^-1 /m^-1
2.0
4.0
6.0
8.0
10.0

ANSWER

The slope represents speed of the wave.

Question 14
(a) When a positively charged conductor is placed near a candle flame, the flame spreads out as shown in the diagram above. Explain this observation. (b)A proton moving with a speed of 5.0 x 10⁵ ms^-1; enters a magnetic field of flux density 0.2 T at an angle of 30° to the field. Calculate the magnitude of the magnetic force exerted on the proton.[proton charge = 1.6X 10^-19C] (c) ) The diagram above illustrates 9.0 V battery of internal resistarIce 0.5Ωconnected to two resistors of values 2.0Ωand R Ω A₁,A₂ and A₃, are ammeters of negligible internal resistances. If A₁ reads 4.0 A, calculate the: (i) equivalent resistance of the combined resistors 2.0Ω and RΩ (ii) currents through A₂ and A₃; (iii) value of R.

Question 14

(a)

When a positively charged conductor is placed near a candle flame, the flame spreads out as shown in the diagram above.
Explain this observation.

(b)A proton moving with a speed of 5.0 x 10⁵ ms^-1; enters a magnetic field of flux density 0.2 T at an angle of 30° to the field. Calculate the magnitude of the magnetic force exerted on the proton.[proton charge = 1.6X 10^-19C]

(c)

)

The diagram above illustrates 9.0 V battery of internal resistarIce 0.5Ωconnected to two resistors of values 2.0Ωand R Ω A₁,A₂ and A₃, are ammeters of negligible internal resistances. If A₁ reads 4.0 A, calculate the:
(i) equivalent resistance of the combined resistors 2.0Ω and RΩ
(ii) currents through A₂ and A₃;
(iii) value of R.

ANSWER

(a)The candle flame ionizes the air around it. .
The positively charged conductor attracts the negative charges in the air and repels the positive charges.

(b)F = qvB Sin θ .
= 1.6 X 10-19 X 5.0 X 105 X 0.2 X Sin 30°
= 0.8 X 10^-1

(c)(i)E = I (Rc + r)
9 = 4(Rc + 0.5)
R: = 9/4-0.5
= 1.75Ω
(ii) Lost volt = Ir = 4.0 X 0.5 =2.0 V
V oltage across 2Ωand RΩ
V = 9.0-2.0 =7.0V
Current in A₂ = I₂ = V/R₂= 7/2 = 3.5A
Current in A₃ =I₃ = V/R = 7/14 = 0.5A
OR
A₃ = A₁ – A₂
= 4.0 – 3.5 = 0.5A
(iii) 1/R_C = 1/R + 1/R2
1/1.75 = 1/R + 1/2
1/R = 1/1.75- 1/2
R = 14Ω

Physics May/June 2010

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