IB Physics SL Paper 2 Question Bank

1.) A student strikes a tennis ball that is initially at rest so that it leaves the racquet at a speed of 57 m s–1. The ball has a mass of 0.068 kg and the contact between the ball and the racquet lasts for 20ms.
a.) Calculate the:
i.) average force exerted on the racquet by the ball
Answer:
F = Δmv / Δt
Substituting the values we have: (0.068 x 57) / (20 x 10-3) – x10-3 because it is ms
F = (0.068 x 57) / (20 x 10-3) = 193.8 N = 194 N

ii.) average power delivered to the ball during impact
Answer:
Power = W / Δt
W (energy) = Kinetic energy = ½ mv2
Power = ½ mv2 / Δt
Substituting the values we have: (0.068 x 57) / (20 x 10-3) – x10-3 because it is ms
F = (0.068 x 57) / (20 x 10-3) = 193.8 N = 194 N

2.) A boy rides a bicycle that is powered by an electric motor. There is a battery that transfers the energy to the electric motor. The emf of the battery is 14 V and it can deliver a charge of 52 kC when it discharges completely from full charge.
a.) The maximum speed that the boy attains is 12 m/s solely with energy from the battery. With this maximum speed, she can cover a distance of 25 km.
i.) Deduce how much time is taken for the battery to discharge. Write it in scientific notation rounded to 3 significant figures.
Answer:
S = distance/time
S = (25 x 1000) / 12 = 2083.33 s = 2.08 x 103 s

ii.) Deduce the average power output of the battery
Answer:
Energy = qV
E = (52 x 103) x 14 = 728000 J = 7.28 x 105 J
Power = Energy / time
P = 7.28 x 105 / 2.08 x 103 = 350 W

iii.) Assuming that all the energy is transferred from the battery to the electric motor, state the resistive forces and determine the total average resistive force that acts on the boy and his bicycle as he rides it. Round to two significant figures
Answer:
Friction and air resistance: Air resistance is faced by both the boy and the bicycle as it acts against the direction he is moving in. Friction is created between the tires of the bicycle and the road.
Power = Force x Speed
Force = 350 / 12 = 29.16666 = 29 N

3.) An ideal monatomic gas is kept in a container of volume 3.1 × 10-4 m3, temperature 310 K and pressure 5.8 × 105 Pa. The volume of the gas as stated before is increased to 7.5 × 10-4 m3 at constant temperature.

a.)Define an ideal gas
Answer:
A gas whose molecules occupy negligible space and have no interactions or intermolecular forces. It is the gas that obeys all gas laws at all temperatures, volumes and pressures. The molecules in an ideal gas have zero potential energy – only kinetic energy.

b.) Determine the number of atoms in the monatomic gas
Answer:
N = pV/kT
N = ((5.8 × 105) x (3.1 × 10-4)) / ((1.38 x 10-23) x 310) = 4.2 x 1022

4.) What is the new pressure of the gas in Pascals round to 3 significant figures in scientific notation
Answer:
p1V1 = p2V2 → p2 = p1V1/V2
p2 = (5.8 × 105 x 3.1 × 10-4) / (7.5 × 10-4) = 239733.3333 Pa
p2 = 2.4 x 105 Pa

5.) Explain the change in pressure with respect to molecular motion
Answer:
While the volume of the gas has increased, it does not alter the average kinetic energy of the molecules. Therefore, molecules don’t collide as frequently with the walls causing the rate of change of momentum to decrease. Because of this, the pressure has decreased as well.

6.) This question is with regards to the thermal properties of matter.
a.) Define thermal capacity and its SI unit.
Answer:
Thermal capacity is defined as the quantity of heat necessary to produce a unit change of temperature in a unit mass of a material. The SI unit is Joule/Kelvin (J/k).

b.) Explain why the temperature of a pure substance does not change during the process of melting (in terms of molecular energy)
Answer:
When energy is given to melt the substance, the solid molecules absorb energy and break the bonds to form a liquid. The heat is absorbed. This only causes an increase in potential energy and not kinetic energy so the temperature remains changed.

7.) There are 2 loudspeakers, X and Y that have the same amplitude at a frequency of 900 Hz. There is a Point P that is located 24.2 m from Speaker X and 26.7 m from Speaker Y. The speed of sound is 340 m/s.

a.) Determine the minimum sound intensity heard at Point P round to 2 significant figures
Answer:
Wavelength = Speed of sound/frequency of the wave
Wavelength = 340/900 = 0.3777 m
To find the sound intensity, the path difference needs to be found.
Therefore, 26.7 – 24.2 = 2.5 m

Intensity = Path difference/wavelength
Intensity = 2.5 / 0.37777 = 6.6177 = 6.6 λ

b.) Define the amplitude and frequency of a wave
Answer:
Amplitude is the distance between the resting position and the maximum displacement of the wave. Frequency is the number of waves passing by a specific point per second.

8.) A proton is moving in a uniform magnetic field with the velocity vector pointing upwards and directed into the plane of the paper.

a.) The path followed by the proton is a circle. Explain why the path is a circle
Answer
The magnetic force is always perpendicular to the velocity vector. Therefore, since the velocity vector is pointing upwards, the magnetic force is towards the left or the center of the circle. Therefore, as long as the velocity vector exists, the magnetic force is centripetal thus causing the proton to move constantly in a circular path.

b.) Explain why the kinetic energy of the proton is constant throughout
Answer
A change in kinetic energy is defined as the work done divided by the force. Hence, if the work done is zero and the force is perpendicular to the velocity, there is no change in kinetic energy therefore making it constant.

9.) The average temperature of ocean surface water is 20 Celsius or approximately 293 Kelvin. Oceans tend to behave as black bodies.
a.) Define black bodies.
Answer
A black body is a perfect absorber and radiator of energy, with no reflecting power.

b.) Describe how the frequency of a black body’s radiation can be utilized to determine the body’s temperature.
Answer
The wavelength of emitted electromagnetic waves depends on the temperature of the emitter. Therefore, the frequency and the color depends on the temperature.

10.) These questions are with respect to the cells.
a.) State the difference between photovoltaic cells and solar heating panels.
Answer
Solar heating panels convert solar energy into thermal energy. However, photovoltaic cells convert solar energy into electrical energy.

b.) There is a farm that uses photovoltaic cells covering an area of 21000 m2. The average solar intensity that falls on the farm is 280 W/m2. The average power output of the farm is 1.4 MW. Determine the efficiency of the photovoltaic cells.
Answer
Power = Intensity x Area
Power = 280 x 21000 = 5.8 MW
Efficiency = Output power/Total power
Efficiency = 1.4 / 5.8 = 0.24 (24%)

11.) This question is regarding atomic physics

a.) Rutherford made a model based on the results of the alpha particle scattering experiment. Describe Rutherford’s model.
Answer
Rutherford’s model proposed that the negatively charged electrons surround the nucleus of an atom. He also claimed that the electrons surrounding the nucleus revolve around it with very high speed in circular paths. He named these circular paths as orbits.

b.) Explain what the binding energy of a nucleus means
Answer
Nuclear binding energy is the energy required to separate an atomic nucleus completely into its constituent protons and neutrons, or, equivalently, the energy that would be liberated by combining individual protons and neutrons into a single nucleus.

c.) Outline why quantities such as binding energy and atomic mass are expressed non SI units
Answer
It is because these quantities would be extremely small

12.) This question is regarding energy resources

a.) State any two renewable energy resources
Answer
Renewable energy is energy derived from natural sources that are replenished at a higher rate than they are consumed. Sunlight and wind, for example, are such sources that are constantly being replenished.

b.) In a nuclear reactor, explain the function of
i.) Heat exchanger
Answer
A heat exchanger is a device that is used to transfer thermal energy from one fluid to another without mixing the two fluids.

ii.) Moderator
Answer
A moderator is a material used in a nuclear reactor to slow down the neutrons produced from fission. By slowing the neutrons down the probability of a neutron interacting with 235U nuclei is greatly increased thereby maintaining the chain reaction.

c.)Which material is generally used as a moderator in the reactor
Answer
Graphite – They reduce the speed of neutrons and allow a nuclear reaction to be sustained

d.) In recent days, it is seen that oil-fired power stations are likely to increase global warming due to the enhanced greenhouse effect.
i.) State what you mean by the enhanced greenhouse effect
Answer
The enhanced greenhouse effect is the impact on the climate from the additional heat retained due to the increased amounts of carbon dioxide and other greenhouse gasses that humans have released into the Earth’s atmosphere since the industrial revolution.

ii.) Explain how greenhouse gasses contribute to global warming
Answer
A greenhouse gas is any gaseous compound in the atmosphere that is capable of absorbing infrared radiation, thereby trapping and holding heat in the atmosphere. By increasing the heat in the atmosphere, greenhouse gasses are responsible for the greenhouse effect (trapping the heat in the atmosphere), which ultimately leads to global warming (the general heating of the Earth).