OCR A Level Physics B (Advancing) Scientific literacy in physics June 2019 question paper H557/02

This question is about momentum and force.

A block of mass 0.20 kg has velocity +1.8 m s^–1. It collides with a stationary block of mass (a) 0.30 kg. The two blocks stick together after the impact.

Calculate the velocity of the two blocks after impact. Ignore the effects of friction.

velocity =........ m s^–1

Show that kinetic energy is not conserved in this collision.

The collision took place over time, t. By calculating the change of momentum of both blocks, show that the force on one block is equal and opposite to the force on the other block, an example of Newton’s third law of motion.

In a crash test, a driverless car strikes a wall and stops. The graph in Fig. 1.1 shows the variation of the force on the car over the time of the collision.

The impulse on the car is given by the area under the curve. Use data from the graph to calculate the initial velocity of the car. Explain your method and reasoning.

mass of car = 1400 kg

initial velocity of car =........ m s^–1

Show that the potential difference across the 4.7 k resistor is 4.2 V to 2 significant figures.

An analogue voltmeter connected across the 4.7 k resistor reads 3.2 V.

Show that the resistance of the voltmeter is about 5 k.

A cell is made by inserting a zinc strip and a copper strip into a potato. When the same analogue voltmeter is connected to the cell as shown in Fig. 2.2, it registers a potential difference of 0.50 V.

Using your answer to (b), calculate the current in the circuit.

When a digital voltmeter of resistance 1.0 M replaces the analogue voltmeter in Fig. 2.2, it registers a potential difference of 0.93 V. Use the readings from the two meters to calculate an estimate for the internal resistance of the potato, stating any assumptions you make.

This question is about electromagnetic induction and eddy currents.

An aluminium disk, mounted horizontally on a low-friction pivot, is placed between the poles of a strong magnet, as shown in Fig. 3.3. There is a uniform magnetic field between the poles of the magnet.

A student sets the disk spinning in the direction shown by the arrow in the plan view above.

Explain how eddy currents are produced in the spinning disk and why these eddy currents make the disk slow down.

The student monitors the slowing of the aluminium disk using light gates to measure the speed of a card fastened to the edge of the disk, as shown in Fig. 3.4.

Fig. 3.5 shows how the speed falls over time.

The student suggests that the speed decreases exponentially.

Explain what the student means by ‘decreases exponentially’ and, using ideas from part (b), explain whether you would expect the speed of the disk to decrease in this way.

Use data from the graph to test whether there is an exponential decrease in speed over time. Make your conclusion clear.

This question is about electrons showing wave-like properties.

An electron is accelerated through a p.d. of 4.3 kV. Calculate the velocity of the accelerated electron. Ignore relativistic effects.

velocity =........ m s^–1

Explain whether it is reasonable to ignore relativistic effects in the calculation in (a)(i) Include a calculation in your explanation.

Calculate the de Broglie wavelength of the accelerated electron.

Accelerated electrons can be diffracted by layers of graphite in a very similar way to light diffracted through a grating. When electrons are accelerated in a glass vessel and pass through graphite, they diffract and form circular rings on a fluorescent screen. Each electron striking the screen emits a tiny flash of light.

Explain why the rings on the screen become smaller and brighter when the accelerating p.d. the electrons pass through is increased.

* Explain how this demonstration shows that electrons can be considered as ‘quantum particles’ showing both wave-like and particle-like behaviour. Your answer should describe which aspects of the demonstration show each type of behaviour and explain how diffraction

effects can be explained using ideas about phasors.

For a stable product, the number of daughter nuclei D at time t is given by the equation

D = N₀ – N

where N₀ is the original number of parent nuclei and N is the number of parent nuclei at time t.

Show that the number of daughter nuclei after time t is given by

The ratio of the number of parent nuclei to number of daughter nuclei can be used to calculate the age of rocks.

The uranium isotope²³⁸₉₂U is the beginning of a ‘radioactive series’ that ends with the stable isotope of lead,²⁰⁶₈₂Pb.

The half-life of the series is 4.47 × 10⁹ years. This means that it will take about 4.5 billion (ii) years before half the uranium-238 (²³⁸U) has decayed into lead-206 (²⁰⁶Pb).

Show that the decay constant for this process is about 1.6 × 10^–10 year^–1.

Use the equation for D given in (c)(i) and the data given to calculate the value for the age of the rock based on the uranium-235 decay series.

Rocks are often dated using three separate decay series. Suggest and explain an advantage of three decay series to date rocks rather than just one.

State how Fig. 6.2 shows that the electric field is uniform within the selector.

A positive charge q moving horizontally through the selector at velocity v as shown in Fig. 6.2 will experience a downwards electric force and an upwards magnetic force.

By considering the forces on the charge, explain why the charge will not be deflected when

Describe and explain the motion of charges moving through the region if their velocities

........

Show that the force on a proton moving at a velocity of 5.2 × 10⁶ m s^–1 at right angles to (i) a field of strength 0.64 T is about 5.3 × 10^–13 N.

Calculate the radius r of the path the proton will follow.

Fig. 7.1 is an image from Mariner 9. It shows most of the crater at the top of Olympus Mons.

Use data from Fig. 7.1 to calculate the resolution of the image.

resolution =........ km pixel^–1

This question is about Martian meteorites (lines 43–47).

Use the value of G and data from the article (lines 56–62) to show that the radius of Mars is about 3.4 × 10⁶ m.

* Calculate the gravitational potential at the surface of Mars and use this value to estimate the energy needed to eject a 0.2 kg rock from the surface to a great distance from the planet. Explain your reasoning.

Use ideas about the gravitational potential of the Sun and the Earth to explain why your calculated value is higher than the energy required for the rock to reach Earth but lower than

the value required for the rock to escape from the Solar System.

An estimate of the atmospheric pressure p at height h above the surface of Mars can be found from the equation

where p_s is the pressure at the average surface level, g is the gravitational field strength at the surface, k the Boltzmann constant and T the temperature of the atmosphere.

The pressure at the top of Olympus Mons is 0.03 kPa. Assuming that the Martian atmosphere is carbon dioxide (mass of one molecule = 7.3 × 10^–26 kg), use the equation given and data from the article (lines 56–62) to calculate an estimate for the height of Olympus Mons above average surface level.

Suggest one reason why this method of estimating the height may be unreliable and explain how this would affect the value of the pressure at the top of Olympus Mons.

Calculation:

Suggestion and explanation:

A large proportion of the radiation absorbed by astronauts comes from high-energy protons in cosmic rays. The American space agency, NASA, estimates that the dose equivalent received by an astronaut on a three-year return trip to Mars is about 1200 mSv. The calculation assumes that the astronaut spends 18 months on the surface of the planet.

The risk of contracting cancer due to radiation exposure is 5% per Sievert. The percentage risk of contracting cancer for an astronaut on a three-year mission to Mars is about 6%. Compare this with the risk for someone on Earth over the same period. Give reasons for the difference in risk on the two planets.

Annual dose equivalent on Earth from cosmic rays = 0.4 mSv.

Explain why exposure to radiation increases the risk of contracting cancer and how the high level of radiation on the surface of Mars may affect the design of the buildings for a human colony on the planet.

Calculate the centripetal force required to keep a 1000 kg ‘shield’ in orbit around the Sun at the L1 point with an orbital period the same as the orbital period of Mars.

Show that the combined gravitational force from the Sun and Mars acting on the ‘shield’ is approximately equal to the centripetal force required.

orbital period of Mars = 5.94 × 10⁷ s mass of Sun = 2.00 × 10³⁰ kg

Suggest why the shield may not remain at the L1 point even though the net force from Mars and the Sun is equal to the centripetal force required.