PHYSICAL SCIENCES - GRADE 12 TERM 3
PAPER 1
MST WALK IN CAMP
MOPANI WEST
WORK, ENERGY AND POWER
QUESTION 1
A 2 kg box is released from rest at point P, 5 m above the ground. It slides down a smooth frictionless
curved track PQ. See the diagram below.
P
5m
2 kg
barrier
Q
10 m
1.1 State the principle of conservation of mechanical energy in words.
R
(2)
1.2 Use the PRINCIPLE OF CONSERVATION OF MECHANICAL ENERGY to calculate the speed of the box
when it reaches point Q. (3)
The box passes point Q and moves 10 m on a rough horizontal surface before striking a barrier at point
R at a speed of 4 ms-1.
1.3 Use ENERGY PRINCIPLES to calculate the magnitude of the average frictional force acting on the box
as it moves from Q to R. (4)
The barrier exerts an impulse of 14 Ns to the LEFT on the box when the box strikes the barrier.
1.4 Calculate the change in kinetic energy of the box after striking the barrier.
(5)
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QUESTION 2
A 12 kg block is initially at rest at point A at the bottom of a ROUGH inclined plane. The block is pulled
up the incline by a constant force F acting parallel to the incline. The block reaches point B, which is at a
vertical height of 4,5 m above the horizontal, with a speed of 2,25 m·s-1 . See the diagram below.
2.1 Define the term non-conservative force. (2)
2.2 Draw a labelled free-body diagram for the block when it is pulled up the inclined plane. (4)
2.3 Calculate the total work done on the block by the NON-CONSERVATIVE forces when the
block moved from point A to point B. (4)
The same constant force F now moves the block at a CONSTANT VELOCITY across a rough
horizontal surface from point B to point C, as shown below. Force F acts parallel to the
horizontal surface.
The magnitude of the constant frictional force acting on the block while moving from point B to point C
is 42 N LARGER than the magnitude of the constant frictional force acting on the block when it moves
from point A to point B.
2.4 Calculate the distance from point A to point B. (5)
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QUESTION 3
A wooden box slides down a rough 8 m long inclined plane AB. The initial velocity of
the box at A is 2 m·s-1 as shown in the diagram below.
3.1 Define a conservative force. (2)
3.2 Name the conservative force in the diagram above. (1)
3.3 State the work-energy theorem in words. (2)
3.4 The velocity of the block at point B is 6,92 m·s-1. Use ENERGY PRINCIPLES
ONLY to calculate the frictional force that the block experiences as it moves
from point A to point B. (4)
3.5 The coefficient of friction for the last horizontal stretch after point B is 0,35.
Calculate the distance the block will travel before coming to a complete stop
without using equations of motion. (4)
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ELECTROSTATICS
QUESTION 1
1.1 A small neutral sphere acquires a charge of -1,95 x 10-6 C.
1.1.1 Were electrons ADDED TO or REMOVED FROM the sphere?
(1)
1.1.2 Calculate the number of electrons which were added or removed.
(3)
1.1.3 Define the term electric field at a point.
(2)
1.1.4 Calculate the magnitude of the electric field at a point 0,5 m from
the centre of the charged sphere.
(3)
1.2 Two point charges, q1 and q2, are fixed 0,02 m apart. The magnitude of charges q1 and q2 is the
same and q1 is NEGATIVELY charged.
The small charged sphere with the charge of -1,95 x 10-6 C is placed at point P, 0,03 m east of charge q2,
as shown in the diagram below. The sphere at point P experiences a net electrostatic force of 1,38 N
west.
Calculate the magnitude of the charge on q2.
(5)
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QUESTION 2
Two identical negatively charged spheres, A and B, having charges of the same magnitude, are placed 0,5
m apart in vacuum. The magnitude of the electrostatic force that one sphere exerts on the other is 1,44
x 10-1N.
2.1 State Coulomb's law in words. (2)
2.2 Calculate the:
2.2.1 Magnitude of the charge on each sphere (4)
2.2.2 Excess number of electrons on sphere B (3)
2.3 P is a point at a distance of 1 m from sphere B.
2.3.1 What is the direction of the net electric field at point P? (1)
2.3.2 Calculate the number of electrons that should be removed from sphere B so that the net electric
field at point P is 3 x 104 N·C-1 to the right.
(8)
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QUESTION 3
A small polystyrene sphere, B, hangs from the ceiling and is attached by a string of
negligible mass. Two other spheres, A and C are suspended on insulated stands. The
charges on each sphere are A = +5,6 nC, B = - 2,34 nC and C = -7,46 nC. The mass
of sphere B is 5,085 x 10-3 kg. Assume that the surfaces of all the three spheres are
conducting.
3.1 Define electrical field strength at a point. (2)
3.2 Sketch the electric field pattern around spheres B and C if A was removed. (3)
3.3 Charge B experiences a net force of 0,004078 N due to charges A and C. Find
the distance, r, between charges B and C. (5)
3.4 Charges A and B are allowed to touch and then moved back to the original
distance between them.
3.4.1 Calculate the new charge on each sphere. (2)
3.4.2 Explain the change, if any, to the field pattern between B and C. (3)
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ELECTRIC CIRCUITS
QUESTION 1
1.1 A group of learners conduct an experiment to determine the emf (ε) and internal resistance (r) of a
battery. They connect a battery to a rheostat (variable resistor), a low resistance ammeter and a
highresistance voltmeter as shown in the diagram below.
The data obtained from the experiment is displayed in the table below.
1.1.1 State ONE factor which must be kept constant during the experiment. (1)
1.1.2 Using the information in the table above, plot the points and draw the line of best fit on a
graph paper. (3)
Use the graph drawn in QUESTION 1.1.2 to determine the following:
1.1.3 Emf (ε) of the battery (1)
1.1.4 Internal resistance of the battery, WITHOUT USING ANY FORM OF THE EQUATION
ε= I(R + r) (3)
1.2 Three electrical devices, X, Y and Z, are connected to a 24 V battery with internal resistance r as
shown in the circuit diagram below. The power rating of each of the devices X and Y are indicated in the
diagram.
With switch S1 closed and S2 open, the devices function as rated. Calculate the:
1.2.1 Current in X (3)
1.2.2 Resistance of Y (3)
1.2.3 Internal resistance of the battery (5)
Now switch S2 is also closed.
1.2.4 Identify device Z which, when placed in the position shown, can still enable X and Y to
operate as rated. Assume that the resistances of all the devices remain unchanged. (1)
1.2.5 Explain how you arrived at the answer to QUESTION 1.2.4. (2)
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QUESTION 2
2.1 Learners want to construct an electric heater using one of two wires, A and B, of
different resistances. They conduct experiments and draw the graphs as shown.
2.1.1 Apart from temperature, write down TWO other factors that the learners
should consider to ensure a fair test when choosing which wire to use. (2) 2.1.2
Assuming all other factors are kept constant, state which ONE of the two wires
will be the most suitable to use in the heater. Use suitable calculations to
clearly how you arrive at the answer. (8)
show
2.2 In the circuit alongside the reading on ammeter A is 0,2 A. The battery has an emf of 9 V and internal
resistance r.
2.2.1 Calculate the current through the 5,5 Ω resistor.(3)
2.2.2 Calculate the internal resistance of the battery. (7)
2.2.3 Will the ammeter reading INCREASE, DECREASE or REMAIN THE SAME if the 5,5 Ω resistor is
removed? Give a reason for the answer.(2)
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QUESTION 3
In the circuit below, the battery has an emf of 24 V and an internal resistance of 0,6 Ω.
The heater has a resistance of 10 Ω and the fixed resistor has a resistance of 30 Ω.
The variable resistor, R, can change between 0 Ω and 15 Ω.
3.1 The variable resistor, R, is set at a resistance of 3,5 Ω.
Calculate:
3.1.1 The total resistance of the circuit (including the battery) (5)
3.1.2 The current measured by ammeter A2 (3)
3.2 The variable resistor is now adjusted to have an even higher resistance value.
How will this affect the power dissipated by the heater? Write only INCREASES,
DECREASES or REMAINS THE SAME. Explain the answer by making use of a
suitable equation. (3)
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QUESTION 4
Learners perform an experiment to determine the internal resistance, r, of a battery.
They use a variable resistor as the external resistance as shown in the diagram below.
Switch S is closed. Readings from the voltmeter and ammeter are recorded after each
change of the resistor.
4.1 Use the information in the table above to plot a graph of potential difference
versus current. Use the graph paper supplied at the end of the question paper. (4)
4.2 Use the graph to determine the following:
4.2.1 The emf of the battery (1)
4.2.2 The internal resistance of the battery
Use an equation to justify the method used. (3)
4.3 A conducting wire of negligible resistance is connected between the points X
and Y. How does this affect the temperature of the battery? Write down only
INCREASES, DECREASES or REMAINS THE SAME.
Explain the answer. (3)
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