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This page covers Questions and Worked Solutions for Physics 9702 Paper 13 October 2020, 9702/13.

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2020 Physics 9702 Paper 13 (pdf)

- What is a reasonable estimate of the volume of a fully inflated standard football?
- What is not an SI base unit?

A coulomb

B kelvin

C kilogram

D second - Which two quantities are both vector quantities?

A displacement and distance

B force and momentum

C torque and time

D weight and pressure - A calibration curve is shown for an ammeter whose scale is inaccurate

Two readings taken on the meter at different times during an experiment are 0.13 mA and 0.47 mA.

By how much did the current really increase between taking the two readings? - A student measures the length l and the period T of oscillation of a simple pendulum. He then uses the equation shown to calculate the acceleration of free fall g.
- An object moves in a straight line. The graph shows the variation with time t of the velocity v of the object.
- An object accelerates uniformly from rest to speed v. It then moves at constant speed v for a time
of 8.0 s before decelerating uniformly to rest. The total time taken is 12.0 s, and the total distance
travelled is 60 m.

What is the speed v ?

- A device for spraying paint consists of a box with its axes horizontal and vertical. One of its vertical faces contains small holes. Paint is fed into the box under pressure via a vertical tube and exits through the holes as fine streams moving horizontally.
- A party balloon is filled with air and held stationary at a height of several metres above the
ground. The balloon is then dropped in still air.

Which statement describes the motion of the balloon from the moment of release until just before it hits the floor? - An object of mass m travelling with speed 5u collides with, and sticks to, an object of mass 5m travelling in the same direction with speed u.
- An air bubble is rising through a liquid at a constant speed. The forces on it are the upthrust U, the viscous drag V and its weight W. Which diagram shows the directions and relative sizes of the forces?
- A couple applies a clockwise torque of 9.0 N m to a circular disc. Which diagram shows this couple?
- A shelf PQ is attached to a vertical wall at P and supports a book.

The shelf is held horizontal by a rigid bar XY, as shown

The weight of the shelf is Ws and the weight of the book is Wb.

The bar is at an angle θ to the shelf and exerts a force F on the shelf.

The shelf is in equilibrium.

What are the magnitudes of the horizontal and the vertical components of the force of the wall on the shelf at P? - A glider is descending at constant speed at an angle of 15° to the horizontal. The diagram shows the directions of the lift L, air resistance R and weight W acting on the glider
- A solid cylinder of density ρ C, cross-sectional area A and length X is submerged in a liquid of density ρ L. The upper face of the cylinder is at a depth H below the surface of the liquid, as shown.
- A ball drops onto a horizontal surface and bounces elastically. What happens to the kinetic energy of the ball during the very short time that it is in contact with the surface?
- Some gas in a cylinder is supplied with thermal energy q. The gas does useful work in expanding at constant pressure p from volume V0 to volume VF, as shown.
- An object of mass 0.30 kg is thrown vertically upwards from the ground with an initial velocity of
8.0 m s
^{–1}. The object reaches a maximum height of 1.9 m. - A water pump raises a mass of 27 × 10
^{3}kg of water through a vertical distance of 80 m in a time of 1.0 hour.

What is the average useful output power of the pump? - A platform is suspended by four steel wires. Each wire is 5.0 m long and has a diameter of
3.0 mm. The Young modulus of steel is 2.1 × 10
^{11}Pa. - A tensile force of 7.00 MN is applied to a sample of steel. This causes the sample to extend by 5.00 mm in the direction of the force. The sample obeys Hooke’s law.
- Two waves X and Y have the same frequency. The amplitude of X is 1.5A
_{0}and the amplitude of Y is 2.5A_{0}. The waves meet at a point and superpose to form a resultant wave. - The displacement–time graph for an air particle in the path of a sound wave is shown.
- A sound wave is displayed on the screen of a cathode-ray oscilloscope (CRO) as shown.
- The horn of a train emits sound of frequency f
_{1}. While the horn is sounding, the train moves directly towards a stationary person. The speed of the train is 0.20v, where v is the speed of sound. - Two satellites in orbit around the Earth are at a constant distance of 100 km apart from each
other.

Satellite X transmits a microwave pulse towards satellite Y. The pulse takes time T to reach Y.

Satellite Y then transmits a pulse of visible light towards satellite X.

What is the time taken for the pulse of light to reach X? - A stationary wave is formed on a stretched string. The diagram illustrates the string at an instant of time when the displacement of the string is at its maximum.
- What is meant by diffraction?
- In a dark room, a small source of red light illuminates two slits that are 0.75 mm apart. A few
metres beyond the slits, the light falls on a screen producing a series of equally spaced bright
lines.

Which change would cause the distance between the bright lines on the screen to be reduced? - Light of wavelength 5.30 × 10
^{–7}m is incident normally on a diffraction grating. The first-order

maximum is observed at an angle of 15.4° to the direction of the incident light.

What is the angle between the first-order and second-order diffraction maxima? - A stationary particle is in an electric field.

The only force on the particle is that from the electric field - A constant potential difference is applied between two horizontal metal plates. A charged oil droplet is held stationary by the electric field between the plates.
- Two resistors R1 and R2 are made from wire of the same material. They are connected in parallel to each other in a circuit, as shown
- A student describes potential difference as the energy transferred per unit charge. Which statement about the energy transfer is correct?
- A metal cube has a resistance of 4.0 between opposite faces. Ten of these cubes are put together to make a cuboid of 1 × 2 × 5 cubes
- A cell is connected to a fixed resistor. Over a long period of time, the internal resistance of the
cell increases.

What is the effect of the increase in internal resistance on the electromotive force (e.m.f.) of the cell and on the power dissipated by the fixed resistor? - Four identical resistors are connected in a circuit, as shown

The battery has negligible internal resistance and an e.m.f. of 30V.

What is the potential difference between the two points X and Y? - A power supply and a solar cell are compared using the potentiometer circuit shown
- The table contains data for four different nuclei P, Q, R and S.
- Which particle is a fundamental particle?

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