# 2020 Physics 9702 Paper 12

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This page covers Questions and Worked Solutions for Physics 9702 Paper 12 October 2020, 9702/12.

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2020 Physics 9702 Paper 12 (pdf)

1. A student uses the volume of a metal coin in order to determine the density of the metal.
What is not needed in order to determine an estimate of the volume of the coin?
A estimate of the diameter
B estimate of the mass
C estimate of the thickness
D use of the formula for the volume of a cylinder
2. The speed v of waves on a stretched wire is given by the equation
v = Tpμq
where T is the tension in the wire and μ is the mass per unit length of the wire.
What are the values of p and q?
3. The diagram shows a force F. P is the horizontal component of F, at an angle θ to F.
Which graph best shows the variation with  of the magnitude of P?
4. A student wishes to measure a distance of about 10 cm to a precision of 0.01 cm.
Which measuring instrument should be used?
5. A steel ball is dropped and falls through a vertical height h. The time t taken to fall is measured using light gates.
6. A stone is thrown vertically upwards from a point X at time t ꞊ 0. The variation with time t of the velocity v of the stone is shown.
7. A mass of 5.0 kg is released from rest on a frictionless surface inclined at 30° to the horizontal. Air resistance is negligible.

1. What is not a statement of one of Newton’s laws of motion?
2. An object falls from a tall building.
The graph shows how the velocity of the object changes with time t
3. Two balls, one of mass 2m and one of mass m, collide.
The diagrams show the initial and final velocities of the balls.
Which collision is not elastic?
4. The diagram shows a ‘ballistic pendulum’.
A pellet of mass m travelling at a speed u hits a stationary block of mass M. The pellet becomes embedded in the block and causes the block to move at a speed v immediately after the impact.
5. A rigid circular disc of radius r has its centre at X. A number of forces of equal magnitude F act at the edge of the disc. All the forces are in the plane of the disc.
Which arrangement of forces provides a total moment of magnitude 2Fr about X?
6. The diagram shows a uniform beam PQ. The length of the beam is 3.0 m and its weight is 50 N. The beam is supported on a pivot 1.0 m from end P. A load of weight W is hung from end P. The beam is in equilibrium.
7. In a high-wire circus act, a man of mass 85 kg is standing at rest at the midpoint of the wire.
8. A cylindrical block of ice of cross-sectional area 12 m2 is floating, partially submerged, in the sea.
The density of the sea water is 1020 kg m-3. A polar bear of mass 400 kg steps onto the block of ice.
9. A ball is thrown vertically upwards. Air resistance is negligible.
Which statement is correct?
10. A hammer with 10 J of kinetic energy hits a nail and pushes it 5.0 mm into a plank.
Both the hammer and nail come to rest after the collision.
What is the approximate average force that acts on the nail while it moves through 5.0 mm?
11. The change in gravitational potential energy E of an object of mass m when moving through height h near the surface of the Earth is given by the equation shown.
12. A racing car has an output power of 300 kW when travelling at a constant speed of 60 m s–1. What is the total resistive force acting on the car?
13. A mass of 60.0 g is suspended from a spring and the distance from the bottom of the spring to the floor is measured to be 16.4 cm.
The mass is replaced with a 100.0 g mass and the distance from the bottom of the spring to the floor is now measured to be 12.6 cm. The spring obeys Hooke’s law.
What is the spring constant of the spring?
14. The graph shows the force–extension graph for a wire
The wire is already extended by a force of 60 N.
How much work is done to increase the extension of the wire by 2.0 mm?
15. The speed v of waves in deep water is given by the equation
16. When sound travels through air, the air particles vibrate. A graph of displacement against time for a single air particle is shown.
17. A vibrating tuning fork is held above a glass cylinder filled to the top with water. The water level is steadily lowered. A loud sound is first heard when the water level is 83.5 cm above the bench. The next loud sound is heard when the water level is 17.1 cm above the bench.
18. An emergency vehicle sounds its siren as it accelerates along a straight road between two points X and Y, as shown in the diagram.
19. Part of the electromagnetic spectrum is shown.
What is the name of the shaded region and what is the order of magnitude of a wavelength of a wave from this region?
20. The three waves shown in each diagram have the same amplitude and frequency but different phase.
They are added together to give a resultant wave.
In which case is the resultant wave zero at this instant?
21. A transmitting mast sends out microwaves of wavelength 1.5 cm and radio waves of wavelength 1.5 km.
A receiving aerial behind a mountain can detect the radio waves but not the microwaves.
22. An experiment is carried out to demonstrate double-slit interference using light of wavelength 500 nm. The distance between bright fringes in the interference pattern is 5 mm.
What are possible values for the distance between the slits and the screen, and the slit separation?
23. Light of a single frequency is incident on a diffraction grating. Seven bright spots are observed on a screen.
Which change will result in an increase in the number of bright spots observed?
24. A molecule behaves as an electric ‘dipole’ consisting of two equal point charges of opposite sign, separated by a fixed distance. The molecule moves with constant horizontal velocity as it enters a vertical uniform electric field, as shown.
The positive and negative charges of the molecule enter the field at the same time.
What describes the effect of the electric field on the velocity of the molecule?
25. Two parallel metal plates are connected to a battery of negligible internal resistance.
One of the plates is slowly moved towards the other.
Which row is correct?
26. Four point charges, each of charge Q, are placed on the edge of an insulating disc of radius r. The disc rotates at a rate of n revolutions per unit time.
What is the equivalent electric current at the edge of the disc?
27. In the circuit shown, a fixed resistor X is connected in series with a battery and a variable resistor
The power dissipated in resistor X is 7.2 W when a current of 3.0A passes through it.
The variable resistor is adjusted so that the power dissipated in X increases by 50%.
What is the new current in the circuit?
28. A resistor and a filament lamp are connected in series with a power supply. The I–V characteristics of the resistor and of the lamp are shown below
The potential difference (p.d.) across the resistor is 3.3V.
What is the resistance of the lamp?
29. A car battery has an electromotive force (e.m.f.) of 12V and an internal resistance of 0.05 ohms. The battery is connected to the starter motor of a car. The current in the motor is 160A.
30. A cell of negligible internal resistance is connected to a network of resistors and a voltmeter, as shown
31. A voltmeter is connected into a circuit with the polarity shown in the diagram
The sliding contact is moved to end P of the potentiometer and then to end Q.
What are the two readings of the voltmeter?
32. What is a conclusion from the alpha-particle scattering experiment?
33. Which particle is a hadron?

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