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exam01_SP10_white-solutions - Exam 1 – white version...

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Unformatted text preview: Exam 1 – white version Physics 2750 SP 2010 Last Name__SOLUTIONS_____ First Name_____________________________ ID # ___________________ This is a closed book exam. I understand, pursuant to University Regulations on academic honesty, that I am not to use any notes or information other than what is in the official, non‐annotated formula sheet. Signature_______________________________________ For multiple choice questions, please make sure that you circle the letter for the answer which you believe to be correct and only that answer. If more than one answer is circled for the same problem, you will not receive credit for it. Don’t get hung up on questions. They should take only one or two minutes each. If you find yourself spending more than a few minutes on a multiple choice question you are probably looking at it the wrong way. You should skip it for now and come back to it later. For full credit show your work for solutions to questions that require calculations. Explain from where you start to solve the problem and show your math flowing from it for full credit. No shown work, no credit! Wherever needed, take the gravitational acceleration to be g = 10 m/s2. Relax, read carefully, think – and then read everything again. During the exam, if you have questions please raise your hand and the TA or the instructor will come to you and provide help. 1. (2 points) A car accelerates from rest on a straight road. A short time later, the car decelerates to a stop and then returns to its original position in a similar manner, by speeding up and then slowing to a stop. Which of the following five coordinate versus time graphs best describes the motion? (2 points) 2. (2 points) An object is shot vertically upward. While it is rising: a) its velocity and acceleration are both upward b) its velocity is upward and its acceleration is downward c) its velocity and acceleration are both downward d) its velocity is downward and its acceleration is upward e) its velocity and acceleration are both decreasing 3. (2 points) Vectors a, b, and c , are related by c = b − a . Which diagram below illustrates this relationship? 4. (2 points) An object, tied to a string, moves in a circle at constant speed as shown. The direction of its velocity and acceleration at point W is: a) →, ↓ b) →, ↑ c) ←, ↓ d) ←, ↑ e) ←, ← 5. (2 points) A girl wishes to swim across a river to a point directly opposite as shown. She can swim at 2 m/s in still water and the river is flowing at 1 m/s. At what angle θ with respect to the line joining the starting and finishing points should she swim? a) 30° b) 45° c) 60° d) 63° e) 90° 6. (2 points)You deserve to have an easy question on this exam because: a) You are awesome. b) You actually came to take the exam. c) You love Big Bang Theory as much as Dorina does. d) You have to tolerate Dorina in class. 7. A time dependent force F = ( −3) i + 2t j (in N), is exerted on a 2 kg object initially at rest. a) Calculate the magnitude of the acceleration of the object at t = 2 seconds. (4 points) b) Calculate the x and y components of the velocity at t = 2 seconds. (4 points) c) Calculate the magnitude and direction of the object’s velocity at t = 2 seconds. Give the angle measured counterclockwise from the positive x‐axis. (2 points) 8. Block A in the figure below weighs 2 N, and block B weighs 5 N. They are connected by a light, flexible cord passing around a fixed, frictionless pulley. The coefficient of kinetic friction between the two blocks is μ = 0.3 and there is no friction with the table. A force F is applied to block B to drag it to the left at constant speed. Take g = 10 m/s2. a) Draw a free body diagram for each box on the axes provided below, clearly indicating all the forces acting on the block. Label each force such that it can be easily identified. Make sure you use the same label for all action‐reaction pair of forces (10 points) Block A Block B y y x x b) Write Newton’s second law (on the x and y axis) for block A. Please use only algebraic symbols (no numbers!) (2 points) c) Write Newton’s second law (on the x and y axis) for block B. Please use only algebraic symbols (no numbers!) (3 points) d) Find the magnitude of the horizontal force F . (4 points) 9. The velocity of a particle starting from rest at time t = 0 sec. and moving along the x axis is given for t > 0 by v = 32t − 2t 3 m/s, where t is in s. a) At what time does the particle achieves its maximum displacement in the positive x direction? (3 points) b) What is the acceleration of the particle at that time? (3 points) c) What is the position of the particle at t = 4 s? (3 points) MC 12/ Q7 10/ Q8 19/ Q9 9/ Total 50/ ...
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