PHYSICAL SCIENCES: PHYSICS (PAPER 1)
GRADE 12
NATIONAL SENIOR CERTIFICATE
NOVEMBER 2019

INSTRUCTIONS AND INFORMATION

1. Write your examination number and centre number in the appropriate spaces on the ANSWER BOOK.
2. This question paper consists of TEN questions. Answer ALL the questions in the ANSWER BOOK.
3. Start EACH question on a NEW page in the ANSWER BOOK.
4. Number the answers correctly according to the numbering system used in this question paper.
5. Leave ONE line between two subquestions, e.g. between QUESTION 2.1 and QUESTION 2.2.
6. You may use a non-programmable calculator.
7. You may use appropriate mathematical instruments.
8. Show ALL formulae and substitutions in ALL calculations.
9. Round off your FINAL numerical answers to a minimum of TWO decimal places.
10. Give brief motivations, discussions, etc. where required.
11. You are advised to use the attached DATA SHEETS.
12. Write neatly and legibly.

QUESTION 1: MULTIPLE-CHOICE QUESTIONS
Various options are provided as possible answers to the following questions. Choose the answer and write only the letter (A–D) next to the question numbers (1.1 to 1.10) in the ANSWER BOOK, e.g. 1.11 E. Each question has only ONE correct answer.
1.1 Which physical quantity is equal to the rate of change of momentum?

1. Mass
2. Impulse
3. Net force
4. Acceleration (2)

1.2 The gravitational acceleration on the surface of a planet of radius R is g.
The gravitational acceleration at a height of 2R above the surface of the same planet is …

1.  9 
    g
2.  4 
    g
3. 4g
4. 9g (2)

1.3 A ball falls from the edge of a table. Ignore the effects of air friction.
Which ONE of the physical quantities associated with the ball during the fall remains constant?

1. Weight
2. Momentum
3. Kinetic energy
4. Gravitational potential energy (2)

1.4 Two trolleys, X and Y, of masses m and 2m respectively, are held together by a compressed spring between them. Initially they are stationary on a horizontal floor, as shown below. Ignore the effects of friction.

The spring is now released and falls to the floor while the trolleys move apart.
The magnitude of the MOMENTUM of trolley X while it moves away is …

1. zero.
2. half the magnitude of the momentum of trolley Y.
3. twice the magnitude of the momentum of trolley Y.
4. the same as the magnitude of the momentum of trolley Y. (2)

1.5 An object is dropped from rest and after falling a distance x, its momentum is p. Ignore the effects of air friction.
The momentum of the object, after it has fallen a distance 2x, is …

1. p
2. √2p
3.  p n
    2
4. 2p (2)

1.6 A police car, with its siren on, is travelling at a constant speed TOWARDS a stationary sound detector. The siren emits sound waves of frequency f and speed v.
Which ONE of the following combinations best describes the frequency and speed of the detected sound waves?

1.7 Two identical spheres, R and S, on insulated stands, carrying charges of +q and -q respectively, are placed a distance apart. Sphere R exerts an electrostatic force of magnitude F on sphere S.

The two spheres are now brought into contact and returned to their original positions.
The magnitude of the electrostatic force that sphere R exerts on sphere S is now …

1. zero
2.  F 
   2
3. F
4. 2F (2)

1.8 Which ONE of the graphs below best represents the relationship between potential difference (V) and current (I) for an ohmic conductor?

1.9 Which ONE of the following combinations regarding the energy conversions in electric motors and electric generators is CORRECT?

(2)
1.10 Consider the statements below regarding the photoelectric effect.
The photoelectric effect proves that …

1. light energy is quantised.
2. light has a particle nature.
3. light has a wave nature.

Which of the statements above is/are CORRECT?

1. (i) only
2. (ii) only
3. (i) and (ii) only
4. (i) and (iii) only (2)
   [20]

QUESTION 2 (Start on a new page.)
Block P, of mass 2 kg, is connected to block Q, of mass 3 kg, by a light inextensible string. Both blocks are on a plane inclined at an angle of 30° to the horizontal.
Block Q is pulled by a constant force of 40 N at an angle of 25° to the incline.
Block P moves on a rough section, AB, of the incline, while block Q moves on a frictionless section, BC, of the incline. See diagram below.

An average constant frictional force of 2,5 N acts on block P as it moves from A to B up the incline.
2.1 State Newton's Second Law in words. (2)
2.2 Draw a labelled free-body diagram for block P. (4)
2.3 Calculate the magnitude of the acceleration of block P while block P is moving on section AB. (8)
2.4 If block P has now passed point B, how will its acceleration compare to that calculated in QUESTION 2.3? Choose from GREATER THAN, SMALLER THAN or EQUAL TO.
Give a reason for the answer. (2)
[16]

QUESTION 3 (Start on a new page.)
Stone A is thrown vertically upwards with a speed of 10 m∙s-1 from the edge of the roof of a 40 m high building, as shown in the diagram below.
Ignore the effects of air friction. Take the ground as reference.

3.1 Define the term free fall. (2)
3.2 Calculate the maximum HEIGHT ABOVE THE GROUND reached by stone A. (4)
3.3 Write down the magnitude and direction of the acceleration of stone A at this maximum height. (2)
Stone B is dropped from rest from the edge of the roof, x seconds after stone A was thrown upwards.
3.4 Stone A passes stone B when the two stones are 29,74 m above the ground.
Calculate the value of x. (6)
3.5 The graphs of position versus time for part of the motion of both stones are shown below.

Which of labels a to h on the graphs above represents EACH of the following?
3.5.1 The time at which stone A has a positive velocity (1)
3.5.2 The maximum height reached by stone A (1)
3.5.3 The time when stone B was dropped (1)
3.5.4 The height at which the stones pass each other (1)
[18]

QUESTION 4 (Start on a new page.)
A bullet moves east at a velocity of 480 m∙s^-1. It hits a wooden block that is fixed to the floor. The bullet takes 0,01 s to move through the stationary block and emerges from the block at a velocity of 80 m∙s^-1 east. See the diagram below.
Ignore the effects of air resistance.
Consider the block-bullet system as an isolated system.

4.1 Explain what is meant by an isolated system as used in Physics. (2)
The magnitude of the momentum of the bullet before it enters the block is 24 kg∙m∙s^-1.
4.2 Calculate the:
4.2.1 Mass of the bullet (3)
4.2.2 Average net force exerted by the wooden block on the bullet (5)
[10]

QUESTION 5 (Start on a new page.)
An object of mass 1,8 kg slides down a rough curved track and passes point A, which is 1,5 m above the ground, at a speed of 0,95 m·s^-1.
The object reaches point B at the bottom of the track at a speed of 4 m·s^-1.

5.1 Define the term conservative force. (2)
5.2 Name the conservative force acting on the object. (1)
5.3 Is mechanical energy conserved as the object slides from point A to point B? Choose from YES or NO. Give a reason for the answer. (2)
5.4 Calculate the gravitational potential energy of the object when it was at point A. (3)
5.5 Using energy principles, calculate the work done by friction on the object as it slides from point A to point B. (4)
Surface BC in the diagram above is frictionless.
5.6 What is the value of the net work done on the object as it slides from point B to point C? (1)
[13]

QUESTION 6 (Start on a new page.)
The siren of a police car, which is travelling at a constant speed along a straight horizontal road, emits sound waves of constant frequency. Detector P is placed inside the police car and detector Q is placed next to the road at a certain distance away from the car. The two detectors record the changes in the air pressure readings caused by the sound waves emitted by the siren as a function of time.
The graphs below were obtained from the recorded results.

6.1 Different patterns are shown above for the same sound wave emitted by the siren. What phenomenon is illustrated by the two detectors showing the different patterns? (1)
The police car is moving AWAY from detector Q.
6.2 Use the graphs and give a reason why it can be confirmed that the police car is moving away from detector Q. (1)
6.3 Calculate the frequency of the sound waves recorded by detector P. (3)
6.4 Use the information in the graphs to calculate the speed of the police car. Take the speed of sound in air as 340 m∙s^-1.(6)
[11]

QUESTION 7 (Start on a new page.)
7.1 A small sphere, Y, carrying an unknown charge, is suspended at the end of a light inextensible string which is attached to a fixed point. Another sphere, X, carrying a charge of +6 x10^-6 C, on an insulated stand is brought close to sphere Y.
Sphere Y experiences an electrostatic force and comes to rest 0,2 m away from sphere X, with the string at an angle of 10° with the vertical, as shown in the diagram below.

7.1.1 What is the nature of the charge on sphere Y? Choose from POSITIVE or NEGATIVE. (1)
7.1.2 Calculate the magnitude of the charge on sphere Y if the magnitude of the electrostatic force acting on it is 3,05 N. (3)
7.1.3 Draw a labelled free-body diagram for sphere Y. (3)
7.1.4 Calculate the magnitude of the tension in the string. (3)
7.2 Two small charged spheres, A and B, on insulated stands, with charges +2 x10^-5 C and -4 x10^-5 C respectively, are placed 0,4 m apart, as shown in the diagram below. M is the midpoint between spheres A and B.

7.2.1 Define the term electric field at a point. (2)
7.2.2 Calculate the net electric field at point M. (6)
[18]

QUESTION 8 (Start on a new page.)
In the circuit diagram below, resistor R, with a resistance of 5,6 Ω, is connected, together with a switch, an ammeter and a high-resistance voltmeter, to a battery with an unknown internal resistance, r.
The resistance of the connecting wires and the ammeter may be ignored.

The graph below shows the potential difference across the terminals of the battery as a function of time.
At time t₁, switch S is closed.

8.1 Define the term emf of a battery (2)
8.2 Write down the value of the emf of the battery. (1)
8.3 When switch S is CLOSED, calculate the:
8.3.1 Current through resistor R (3)
8.3.2 Power dissipated in resistor R (3)
8.3.3 Internal resistance, r, of the battery (3)
8.4 Two IDENTICAL resistors, each with resistance X, are now connected in the same circuit with switch S closed, as shown below.

The ammeter reading now increases to 4 A.
8.4.1 How would the voltmeter reading change? Choose from INCREASES, DECREASES or REMAINS THE SAME.
Give a reason for the answer by referring to Vinternal resistance. (2)
8.4.2 Calculate resistance X. (5)
[19]

QUESTION 9 (Start on a new page.)
9.1 A simplified diagram of an electric generator is shown below. When the coil is rotated with a constant speed, an emf is induced in the coil.

9.1.1 Is this an AC generator or a DC generator? (1)
9.1.2 Briefly explain how an emf is generated in the coil when the coil is rotated by referring to the principle of electromagnetic induction. (2)
9.1.3 Draw a sketch graph of the output voltage versus time for this generator. Show ONE complete cycle. (2)
9.2 A 200 Ω resistor is connected to a DC voltage supply, as shown in diagram A. The energy dissipated in the resistor in 10 s is 500 J.
The same resistor is now connected to an AC source (diagram B) and 500 J of energy is also dissipated in the resistor in 10 s.

9.2.1 Define the term rms voltage of an AC source. (2)
9.2.2 Calculate the maximum (peak) voltage of the AC source. (5)
[12]

QUESTION 10 (Start on a new page.)
During an experiment, light of different frequencies is radiated onto a silver cathode of a photocell and the corresponding maximum speed of the ejected photoelectrons are measured.
A graph of the energy of the incident photons versus the square of the maximum speed of the ejected photoelectrons is shown below.

10.1 Define the term photoelectric effect. (2)
Use the graph to answer the following questions.
10.2 Write down the value of the work function of silver.
Use a relevant equation to justify the answer. (3)
10.3 Which physical quantity can be determined from the gradient of the graph? (1)
10.4 Calculate the value of X as shown on the graph. (5)
The experiment above is now repeated using light of higher intensity.
10.5 How will EACH of the following be affected? Choose from INCREASES, DECREASES or REMAINS THE SAME.
10.5.1 The gradient of the graph (1)
10.5.2 The number of photoelectrons emitted per unit time (1)
[13]
TOTAL: 150

DATA FOR PHYSICAL SCIENCES GRADE 12 PAPER 1 (PHYSICS)
TABLE 1: PHYSICAL CONSTANTS

TABLE 2:  FORMULAE