2022, Prova 2

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1. 

   QUESTION 1 (2 marks) Two spaceports are stationary relative to each other. Astronaut A moves from one spaceport to the other at relativistic speed and observes the lights on both spaceports turn off at the same time. Astronaut B is at a stationary position equally distant relative to each spaceport and observes the lights turn off one after the other. Explain why the astronauts view these events differently.

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2. 

   QUESTION 2 (2 marks) Contrast the properties of up quarks and tau particles.

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3. 

   QUESTION 3 (8 marks) Negatively charged oil drops were placed in a uniform electric field generated by two parallel plates. By altering the applied voltage between the plates, the oil drops were suspended in the air between the plates. + + + + + − − − − − oil drop − + Not to scale The graph shows the electric field strength required (achieved by altering the applied voltage) to suspend negatively charged oil drops of varying weight. 10 20 30 40 0 Oil drop weight (N) 50 60 3.0 0.5 0.0 Electrical field strength (1019 V m−1) 1.5 1.0 2.5 2.0 3.5 a) Determine the average charge on the oil drops. Show your working. [4 marks] Average charge = C (to two significant figures) Another oil drop was suspended between the plates with an electric field strength of 2.0 × 1019 V m−1. b) Determine the work done to move this oil drop a distance of 5 mm towards the negatively charged plate. Show your working. [4 marks] Work done = J (to two significant figures)

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4. 

   QUESTION 4 (5 marks) A stationary object on a frictionless inclined plane is connected to a 15 kg weight as shown. 35º 15 kg Not to scale Calculate the mass of the object on the inclined plane. Mass = kg (to two significant figures)

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5. 

   QUESTION 5 (3 marks) The Feynman diagram for a particle interaction is shown. Space Time e− e− e+ γ e+ Describe the particle interaction taking place.

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6. 

   QUESTION 6 (14 marks) A light was shone onto a metallic surface and the subsequently released photoelectron passed through a magnetic field. Metal surface Magnetic field going into the page Light source a) Identify the direction the photoelectron would have curved as it passed through the magnetic field. [1 mark] The graph shows the maximum kinetic energy of the photoelectron as the frequency of the light was changed. 1.7 1.8 1.9 2.0 1.6 1/λ (106 m−1) 2.1 2.2 1.2 0.2 0.0 Maximum kinetic energy (eV) 0.6 0.4 1.0 0.8 1.4 2.3 2.4 2.5 2.6 b) Determine the work function for the metal. Show your working. [4 marks] Work function = J (to two significant figures) c) If the strength of the magnetic field is 5 µT, determine the maximum radius of the photoelectron’s path through the magnetic field, when light of wavelength 450 nm was shone onto the metallic surface. Show your working. [9 marks] Radius = m (to two significant figures)

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7. 

   QUESTION 7 (3 marks) Two asteroids experience a gravitational force of 3.3 × 103 N between them. Their masses are 2.7 × 1017 kg and 6.1 × 1015 kg. Calculate the distance between the two asteroids. Show your working. Distance = m (to two significant figures)

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8. 

   QUESTION 8 (4 marks) The graph shows the gravitational force experienced by a rocket of mass 750 kg as it approaches an asteroid. 5 10 15 20 0 1/r2 (10−13 m−2) 25 30 30 5 0 Gravitational force on rocket (N) 15 10 25 20 35 40 45 50 Determine the mass of the asteroid. Show your working. Mass = kg (to two significant figures) DO NOT WRITE ON THIS PAGE THIS PAGE WILL NOT BE MARKED CONTINUE TO THE NEXT PAGE

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9. 

   QUESTION 9 (9 marks) A person spins an object 4.3 m above the ground in a horizontal circular path of radius 0.8 m. They release the object horizontally, allowing it to travel to the ground. a) Calculate the centripetal acceleration of the object before it is released, given it takes 5 s for the object to complete 12 revolutions. Show your working. [4 marks] Centripetal acceleration = m s−2 (to two significant figures) b) Calculate the total horizontal displacement for the object after it is released. Show your working. [5 marks] Total horizontal displacement = m (to two significant figures)

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