A Level Physics 9702 Paper 21, May/June 2025

Define acceleration.

In an experiment, two objects A and B are released from the side of a building, as shown in Fig. 1.1. Object A is released from rest at a height of 14 m above the horizontal ground. Object B is released with an initial upwards vertical velocity $u$ at a height of 3.6 m above the ground. Both objects take the same time to reach the ground and they do not collide with each other. Air resistance is negligible. Calculate the time taken for object A to reach the ground.

Use your answer in (b)(i) to calculate $u$.

In a second experiment, object B is released from the same height and given the same initial speed as in (b) but at a release angle $\theta$ to the vertical, as shown in Fig. 1.2. State and explain whether the time taken for object B to reach the ground is less than, the same as or greater than the time in (b)(i).

By considering energy, state and explain the effect of the change in release angle on the speed at which B reaches the ground.

State the principle of moments.

Three objects A, B and C are placed on a horizontal beam. The beam is in equilibrium, as shown in Fig. 2.1. The beam is uniform and has length 6.0 m. The pivot is at the midpoint of the beam. Object A has mass 60 kg and is at one end of the beam. Object B has mass 45 kg and is at a distance $x$ from the pivot. Object C has mass 80 kg and is at the other end of the beam. Calculate $x$.

The beam is 0.80 m above horizontal ground. Object A is removed and replaced by a spring connected to the ground and the beam, as shown in Fig. 2.2. After the change, the beam is again horizontal and in equilibrium. The positions of B and C are unchanged. The spring has an unstretched length of 0.59 m and obeys Hooke's law. Calculate the spring constant of the spring.

Calculate the elastic potential energy of the spring.

Define power.

An electric car is powered by a motor. The car is travelling at a constant speed of $35{\text{ m s}}^{-1}$ along a straight horizontal road, as shown in Fig. 3.1. There is a total resistive force of 1750 N acting on the car. Calculate the power transmitted to the wheels of the car by the motor.

Calculate the useful work done by the motor when the car travels a distance of 17 km.

The potential difference (p.d.) across the motor has a constant value of 600 V and the motor has an efficiency of 85%. Calculate the current in the motor.

The car in (b) now reaches a slope, as shown in Fig. 3.2. The car continues down the slope at the same speed as in (b). State and explain the effect, if any, of the slope on: the air resistance acting on the car

the current in the motor.

State the principle of superposition.

Light of wavelength $7.2\times {10}^{-7}\text{ m}$ is incident normally on a double slit, as shown in Fig. 4.1. A screen is at a distance $D$ from the double slit. The double slit and the screen are parallel. The separation of the slits in the double-slit arrangement is 0.16 mm. The resulting interference pattern on the screen contains nine dark fringes, as shown in Fig. 4.2. The distance between the centres of the first and ninth dark fringes is 3.2 cm. Calculate $D$.

The slit separation is now gradually decreased from 0.16 mm to 0.04 mm. The distance between the centres of adjacent dark fringes is $x$. On Fig. 4.3, sketch the variation of $x$ with slit separation.

Use the definitions of speed $v$, frequency $f$ and wavelength $\lambda$ to derive the wave equation $$v=f\lambda \text{.}$$

A source of sound waves of frequency 236 Hz is travelling at a constant velocity of $20{\text{ m s}}^{-1}$. A stationary observer has a microphone connected to a cathode-ray oscilloscope (CRO). The microphone detects the sound waves as the source moves directly towards the observer. The resulting trace on the CRO is shown in Fig. 5.1. The time-base on the CRO is set to $1.0{\text{ ms div}}^{-1}$. Calculate the frequency of the sound waves detected by the microphone.

Determine the speed of the sound in air.

Calculate the current in X.

The number density of charge carriers (electrons) in nichrome is $8.5\times {10}^{28}{\text{ m}}^{-3}$. Calculate the average drift speed of the charge carriers in X.

Calculate the resistivity of the nichrome.

Wire Y is identical to wire X. Wire Y is added to the circuit in parallel with wire X, as shown in Fig. 6.2. State and explain the effect, if any, of this change on: the reading on the ammeter

the average drift speed of the charge carriers in X.

Nitrogen-12 (${}_7^{12}\text{N}$) is an unstable isotope of nitrogen that decays by the emission of radiation to carbon-12 (${}_6^{12}\text{C}$). Complete the full nuclear equation for the decay, including all the particles involved. $${}_7^{12}\text{N}\to$$

Hydrogen-1 (${}_1^1\text{H}$) is an isotope of hydrogen. An atom of hydrogen-1 comprises a proton with an orbiting electron. An antiparticle equivalent of hydrogen-1 comprises an antiproton with an orbiting positron. The antiquarks in the antiproton are the antiparticles of the quarks in a proton. State the charge on the positron in terms of the elementary charge $e$.

State the group (class) of fundamental particle to which the positron belongs.

In Table 7.1, state the flavour and charge of the three antiquarks that comprise the antiproton. Table 7.1