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Unformatted text preview: Exam 2 – White version Physics 2750 Spring 2010 Last Name______________________________ 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. i j 1. (2 points) Steve pushes a stalled car with a force F 210 30 (in N). The displacement of the car is 10 (in meters). How much work does Steve do? x 5i j
a) b) c) d) e) 1350 J ‐1350 J 0 J 2250 J ‐2250 J 2. (2 points) A force parallel to the x‐axis acts on a particle moving along the x‐axis. This force produces a potential energy given by U x 2 x 3 . What is the force acting on the particle when it is at x = ‐ 0.4 m? a) b) c) d) e) 0.24 N ‐0.24 N ‐0.96 N 0.96 N 0.08 N 3. (2 points) When a certain rubber band is stretched a distance x, it exerts a restoring force of magnitude F ax bx 2 , where a and b are constants. The work done in stretching this rubber band from x = 0 to x = L is: a) aL2 bL3 b) aL 2bL2 c) a 2bL d) bL e) aL2 / 2 bL3 / 3 4. (2 points) As a particle moves along the x axis it is acted upon by a conservative force. The potential energy is shown below as a function of the coordinate x of the particle. Rank the labeled regions according to the magnitude of the force, least to greatest. a) AB, BC, CD b) AB, CD, BC c) BC, CD, AB d) BC, AB, CD e) CD, BC, AB 5. (2 points) Sphere X, of mass 2 kg, is moving to the right at 10 m/s. Sphere Y, of mass 4 kg, is moving to the left at 10 m/s. The two spheres collide head‐on. The magnitude of the impulse of X on Y is: a) twice the magnitude of the impulse of Y on X b) half the magnitude of the impulse of Y on X c) one‐fourth the magnitude of the impulse of Y on X d) four times the magnitude of the impulse of Y on X e) the same as the magnitude of the impulse of Y on X 6. An object with mass m1 = 5 kg moving with a speed v1 = 60 m/s collides with an object of mass m2 = 2 kg initially at rest. After the collision each of the objects has a velocity (not equal though) that is directed 30° from the original direction of motion of the 5 kg. a) Make a drawing for theproblem and clearly indicate the direction of the velocity for each of the two objects after collision. (2 points) b) Calculate the linear momentum of the system before collision. (2 points) c) What is the speed of the 2 kg particle after the collision? (6 points) A rifle bullet with mass m1 = 8.0 g moving at 800 m/s strikes and embeds itself in a block with mass m2 = 0.992 kg that rests on a rough, horizontal surface with a coefficient of friction = 0.2 and is attached to a coil spring of elastic constant k = 200 N/m. a) Find the speed of the block + bullet system immediately after the impact. (3 points) b) What is the maximum compression of the spring? (7 points) 7. A 4.0-kg ball is on the end of a 1.6-m rope which is fixed at point 0. The ball is held at A, with the rope horizontal, and is given an initial downward velocity v0. The ball moves through three quarters of a circle and arrives at B, with the rope barely under tension. Take g = 10 m/s2. a) Find the velocity of the ball at point B. (4 points) b) Find the initial velocity of the ball at point A. (6 points) MC 10/ Q6 10/ Q7 10/ Q8 10/ Total 40/ ...
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