PHY 183 Mock Individual Exam #1 Spring 2017

Transcription

1 Answer the questions in the spaces provided on the question sheets. If you run out of room for an answer, continue on the pages marked Extra Work, but indicate that you have done so. Your answers should include explanations where necessary (or requested) as well as appropriate units and labels. Write legibly If we can t read it, we can t grade it. If you have a question, ask your instructor not your classmate. This part of the exam is to be completed alone without the aid of your group members or other outside resources. A formula sheet has been provided for you. By signing below, you are agreeing that you have not received unauthorized assistance during this exam, which includes but is not limited to crib sheets & note cards, course notes, and other stored formulas. Name (print legibly): Signature: Question Points Bonus Points Score Total: 125 0

2 Extra Work (Please indicate which problem part you are solving here.)

3 1. Below is a snippet of VPython code that is meant to model the motion of a puck sliding on a horizontal sheet of ice that is being acted on by a net force. The net force points entirely parallel to the sheet of ice. We removed the set up lines, which are not relevant for the physics. #Objects Puck = cylinder(pos=vector(0,0,0), radius=0.1) #Parameters and Initial Conditions mpuck = 0.2 vpuck = vector(1,2,0) ppuck = mpuck*vpuck #Time and time step t = 0 tf = 10 dt = 0.01 #Calculation Loop while t<tf: rate(100) Fnet = vector(2,2,0) ppuck = ppuck + Fnet*dt Puck.pos = Puck.pos + (ppuck/mpuck)*dt t = t + dt (a) (10 points) What is the initial momentum of the puck? Answer with numbers in vector form. Explain how you came to this conclusion.

4 (b) (5 points) Of what use is the Calculation Loop in the code? Be as specific and concise as possible. (c) (5 points) According to the code, what direction does the net force point? Answer with numbers in unit vector form. (d) (5 points) According to the code, by how much does the y-component of the Puck s momentum change in the first loop of the Calculation Loop? Answer in numbers. Explain how you came to this conclusion.

5 2. A perfectly spherical asteroid of diameter 579 km travels between the earth and the moon [see diagram below] Moon Earth Asteroid. (a) (6 points) Describe and list all of the forces acting on all 3 bodies in this scenario [note: describe in this case means to indicate the origin of the force]. (b) (5 points) If the mass of the asteroid is kg what is the acceleration due to gravity if you where on the surface of the asteroid?

6 (c) (4 points) With the acceleration you calculated describe what would happen if a person jumped vertically upwards on the asteroid? (d) (5 points) What is the magnitude of the force being exerted on the asteroid by the planet Earth if the asteroid is a distance of km from the center of the Earth? (e) (5 points) If the asteroid is travelling at a velocity of m/s, will the asteroid enter into a circular orbit around the Earth? Please provide evidence for your conclusion.

7 3. A Barbie jeep and a regular truck are driving next to each other on a flat piece of land. The Barbie jeep has a constant velocity of 4 m/s moving North, while the truck, driving parallel to the jeep, moves at a constant velocity of 20 m/s and 45 degrees Northwest. There is a spectator standing directly behind both of the vehicles as they drive. (Consider North +y and East +x). (a) (5 points) Draw a diagram roughly representing the two vectors if the dot below is the spectator. (b) (5 points) What is the vector velocity of the truck relative to the Barbie jeep?

8 (c) (5 points) A strong, Northern gust of wind changes the velocity of the Barbie jeep from (0, 4) m/s to (0, 8) m/s after 2 seconds. What is the vector force of the wind on the jeep if the toys mass is 20 kg? (d) (5 points) In the same amount of time and with the same force calculated in part C, what is the final momentum of the 4000 kg truck relative to the spectator as it continues moving Northwest?

9 (e) (5 points) The vehicles are now being observed driving on a planet with an acceleration due to gravity twice that of the Earths. Does this change the velocities of the cars calculated from the previous parts of this question? If yes, explain which part; if not, explain your answer.

10 4. Falcon is flying back to the Avenger base when his suit malfunctions. His suit is only providing a force of (0,1332) N. Antman has offered to help repair the electronics, but needs to know how long he has before Falcon hits the ground. He was 750 m above the ground when the suit stops working. Falcon has a mass of 136 kg. (a) (5 points) How long before Falcon hits the ground? (b) (5 points) Antman is having trouble fixing the suit, and Falcon would like to know his total velocity when he hits the ground so he is prepared for how much it will hurt. His initial velocity was (15,0) m/s (c) (5 points) Find how far Falcon will travel in the x-direction before hitting the ground so the medical rescue team knows where to meet him.

11 (d) (5 points) Draw a graph of Falcons position (y direction) vs. time and his velocity vs. time. (e) (5 points) Antman says he is unable to fix the suit, but suggests removing the mass of the unessential parts of Falcons suit so that the pull of gravity will be less and he wont accelerate as fast. Is Antman right? Why or why not?

12 5. You are an intern working on the new Spiderman movie Spiderman Homecoming as part of the stunt team. The stunt coordinator Zoe Bell has tasked you with working on the webbing for a scene in which Spiderman is holding a safe which has been pushed out of the top floor of a building. The Young s modulus for the wire is 210 GPa. Zoe wants to make sure you know your physics about wires before letting you help design the stunt. (a) (6 points) If the mass of the safe that they want to use for the stunt is 3204kg (which was one of the masses the safe was tested with) and the radius of the wire is.5cm, compute the stress on the wire. (b) (6 points) Draw a free-body diagram of the forces acting on the safe. (c) (6 points) If the wire s original length is 2m, how much has it stretched by when the safe is attached to it?

13 (d) (7 points) If the bond length of the material is m compute the interatomic spring stiffness of the wire.

14 Extra Work (Please indicate which problem part you are solving here.)