辅导案例-PHS1001

  • July 9, 2020

1 Semester One 2020 Examination Period Faculty of Science School of Physics and Astronomy UNIT CODES: PHS1001 TITLE OF PAPER: Foundation Physics – Paper 1 of 1 EXAM DURATION: 12 hours THIS PAPER IS FOR STUDENTS STUDYING AT: (tick where applicable) Caulfield Clayton Parkville Peninsula Monash Extension Off Campus Learning Malaysia Sth Africa Other (specify) No examination materials are to be shared with others. This includes retaining, copying, memorising or noting down content of exam material to share with any other person by any means during or following your exam. Failure to comply with the above instructions, or attempting to cheat or cheating in an exam may be a discipline offence under Part 7 of the Monash University (Council) Regulations, or a breach of instructions under Part 3 of the Monash University (Academic Board) Regulations. AUTHORISED MATERIALS OPEN BOOK YES NO CALCULATORS YES NO SPECIFICALLY PERMITTED ITEMS YES NO This exam is an open book take-home exam: you may refer to any materials (paper-based or electronic, including those available on the unit’s Moodle site) and use any calculators and software tools. The only restriction is that the work must be your own you are not allowed assistance from other people, including (but not limited to) fellow students. 1. This paper is a pdf on 15 pages including this one and a copy of the exam coversheet. Please check that all pages are present. 2. This paper has 3 sections: Section A – Mechanics, Section B – Electricity and Magnetism, and Section C – Waves, Rays, and Quantum. There are 40 marks in Section A, 30 marks in Section B, and 30 marks in Section C. 3. Please answer by producing a pdf of your responses and submitting them to moodle. Aim for pages of consistent A4 size. This may be photographs of handwritten work, a typeset electronic document, or any other method of you recording your work, or any combination of such methods. If you use photographs of handwritten work, ensure that they are of easily legible quality and resolution. 4. We suggest that you either print out this exam, use the exam booklet provided in Moodle or write on your own blank paper. If you use blank paper clearly write the section on each page, the question and then your answers. 5. Write your Student ID number, Surname, and First Name, on the non-Invigilated Exam Coversheet on the next page. Ensure that you have read and understood the Preamble on the coversheet regarding Honour and Integrity in Assessment and the Student Statement. 6. Always include appropriate units in your final answer. 7. You are advised to show your working. Remember to explain any symbols not in the information provided. Rough (preliminary) working may be done on the left hand pages of your script book. (If you use a software tool, you may want to explain the use of the tool or include a copy of a formula or code that you fed into the tool.) 2 3 PHS1001 2020 Exam SECTION A – Mechanics (4 Questions worth a total of 40 Marks) A1. 10 Marks (2+2+2+2+2) A woman is launched from a waterslide into the air at an angle of 50º. With no wind she would travel 40m horizontally where she lands in a water pool. The time she is in the air is 3.1s. (a) What is her initial horizontal velocity at launch? ( 2 Marks) Solution: (b) What is the magnitude of the velocity at launch? (2 Marks) Solution: (c) What is her vertical velocity at landing? (2 Marks) Solution: (d) What is the magnitude of the velocity at landing? Calculate this from your answers in (a) and (c). Justify your answer. (2 Marks) Solution: (e) If when she is near her maximum height she experiences a brief gust of wind that instantaneously reduces her horizontal velocity by 2.9m/s. What distance does she travel horizontally? (2 Marks) Solution: 4 A2. 10 Marks (2+2+1+1+2+2) A car with snow tyres (m=1500 kg) is sliding down an icy hill with a slope of 15º at an initial speed of 8 m/s. (a) Draw a free-body diagram of the car on the hill. You must label all forces. (2 Marks) Solution: (b) What coefficient of kinetic friction, k, will result in the acceleration being 0 m/s2? (2 Marks) Solution: (c) If the coefficient of kinetic friction is actually k=0.4 what is the cars acceleration? (1 Mark) Solution: (d) What is the stopping distance? (1 Marks) Solution: (e) After sliding 12 m what is the momentum of the car? (2 Marks) Solution: 5 (f) At this point of having travelled 12m the car collides into another car (m=1000 kg) travelling 3 m/s in the same direction down the slope and they are stuck together. What is the velocity just after impact? (2 Marks) Solution: A3. 10 Marks (2+4+2+2) A skater encounters a 6m long ramp with a 20º upward incline. The mass of the skater (including skateboard) is 75kg. The coefficient of rolling friction between the skateboard wheels and the ramp is 0.025. (a) What is the thermal energy generated between the wheels and the ramp as the skater moves to the top of the ramp? (2 Marks) Solution: (b) At what speed must the skater start up the ramp to reach the top still moving at 3.5 m/s? You must solve this problem with conservation of energy. (4 Marks) Solution: 6 (c) At the speed you calculated in (b) what is the mechanical energy of the skater at the start of the ramp? (2 Marks) Solution: (d) What percentage of the skater’s mechanical energy is “lost” to friction? (2 Marks) Solution: A4. 10 Marks (3+5+2) A 5 m long ladder leans against a frictionless wall at an angle of 54º as shown below. (a) From the diagram above write down expressions for the x and y components of translational equilibrium and for rotational equilibrium. The pivot point should be at the base of the ladder (3 Marks) Solution: 7 (b) Using the expressions for translational and rotational equilibrium in (a) what is the minimum value of the coefficient of static friction, s, with the ground that prevents the ladder slipping? (5 Marks) Solution: (c) If the ground you placed the ladder on was icy with a coefficient of static friction of s=0.1 what is the smallest angle you could place the ladder without it slipping? (2 Marks) Solution: END OF SECTION A 8 SECTION B Electricity and Magnetism (3 Questions worth a total of 30 Marks) B1. 10 marks (3+2+5) A circuit is set up consisting of three resistors combined in different ways, with no battery or power supply attached, but with a uniform magnetic field pointing up out of the plane of the circuit in a small by region , as shown below. a) Determine an expression for the effective resistance of the circuit. (3 marks) Solution: b) What value of 3 would make the effective resistance of the circuit equal to 1? Conceptually explain why this works. (2 marks) Solution: c) If the effective resistance is 5 kΩ, = 0.03 m and = 0.02 m and we power the circuit by making the B field increase by 5T every second, what is the current in the circuit. Give both the magnitude and direction of the current. (5 marks) Solution: R1 R2 R3 9 B2. 10 marks (3+2+5) An electron and a proton are both accelerated from rest across a potential difference with magnitude || = 5 V. a) How fast is each particle going after being accelerated across the potential, i.e., after leaving the region with the potential? (3 marks) Solution: The particles are then sent moving at these speeds towards the right into a region of uniform magnetic field directed into the page and with an electric field directed downward as shown below: The electron continues straight to the right through the region. b) What happens to the proton as it enters the region with the fields? (Does it go straight or is it deflected? If deflected, in what direction is it deflected? Also justify your answer). (2 marks) Solution: X X X X X X X X X X X X X X X X X X X X X X X X E B V 10 (c) Suppose now you accidentally bump the experimental setup, and as a result change the field strengths and launch an electron into the region with the fields with a speed of 750 km/s at a direction 40 degrees from the horizontal (see figure below). If the new field strengths are E=1000 N/C and B =250 mT, what is the net force (magnitude and direction) on the electron as it enters the fields? (5 marks) Solution: B3. 10 marks (1+4+2+3) A proton is given a speed of 30 km/s and sent towards a charge of 1 nC which is fixed in place 30 m away. a) What is the value of the potential 30 m away from the 1 nC charge? (1 mark) Solution: b) What is the closest that the proton gets to the 1 nC charge? (4 marks) Solution: X X X X X X X X X X X X X X X X X X X X X X X X E B V (=750km/s) 40o 11 (c) If we do this with an electron moving at 30km/s and a -1nC charge 30m away, does the electron get closer to the -1 nC charge than the proton gets to the +1 nC charge? You may answer this either with a calculation or a conceptual argument. (2 marks) Solution: (d) Sketch equipotential lines for the case of the proton near the 1nC charge. Be sure to indicate the potential close to each individual charge, at moderate distances from the charges and also very far from both of them. (3 marks) Solution: END OF SECTION B 12 SECTION C Waves, Rays and Quantum (3 Questions worth a total of 30 Marks) C1. 10 marks (1+1+1+1+2+4) (a) What is the amplitude of the wave? (1 mark) Solution: (b) What is the wavelength of the wave? (1 mark) Solution: (c) What is the period of the wave? (1 mark) Solution: (d) What is the velocity of the wave? (1 mark) Solution: (e) What is the phase constant for the wave? (2 mark) Solution: 13 Assume the wave we have been discussing is moving to the right, and suppose a second wave described by (, ) = ( 2 + 2 ) is also present. (f) Describe or sketch the superposition of the two waves as a function of x from x=0 to 4, for t=0.5s, taking care to justify your claims or sketch. (4 marks) Solution: C2. 10 marks (3+3+2+2) Consider the following system of a diverging lens and converging lens, both with focal lengths of 2 cm. (a) Draw, on the diagram below, the three special rays to determine where the image of the object at x=0 ends up after travelling through the diverging lens. Be sure to identify the point where the image is formed. (3 marks) Solution: 14 (b) Draw, on the diagram below, the three special rays to determine where the image (of the image created by the diverging lens) ends up after going through the converging lens. Be sure to identify the point where the image is formed. (3 marks) Solution: (c) What is the overall magnification? (2 marks) Solution: (d) How does this result compare to the image that would have resulted without the diverging lens present? Consider both the location and magnification of the final image. (2 marks) Solution: 15 C3. 10 marks (1+3+2+4) A stream of electrons travelling at 40.0 km/s is incident on a single slit of width 500.0 nm. (a) What is wavelength of the electrons? (1 mark) Solution: (b) What is the spacing between adjacent minima in the resulting diffraction pattern if there is a screen 1.20 metres behind the slit? (3 marks) Solution: (c) If the electrons were instead sent one at a time (but still many sent), rather than as a stream, would a diffraction pattern still be seen? Why or why not? (2 marks) Solution: (d) If these electrons were ejected from a piece of Titanium with a work function of 3.84 eV via the photoelectric effect, what was the wavelength of the light used? (4 marks) Solution: END OF EXAM

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