Physics I Exam 2 Spring 2015 (version A)

Transcription

1 Physics I Exam Spring 015 (version A) Section Number Section instructor Last/First Name (PRINT) / Last 3 Digits of Student ID Number: Answer all questions, beginning each new question in the space provided. Show all work. Show all formulas used for each problem prior to substitution of numbers. Label diagrams and include appropriate units for your answers. Write your name and section number at the top of each page in the space provided and write the name of your section instructor in the place provided in the cover sheet.you may use an alphanumeric calculator (one which exhibits physical formulas) during the exam as long as you do not program any formulas into memory. By using an alphanumeric calculator you agree to allow us to check its memory during the exam. Simple scientific calculators are always appropriate! Formula Sheets are the last two pages of the exam. For your convenience you may carefully remove it from the Exam. Please take it with you at the end of the exam or throw it in a waste basket. Be Prepared to Show your Student ID Card Score on each problem: I. (0) II. (30) III. (30) IV. (0) Total Score (out of 100 pts)

2 Last Name only (PRINT) Part I. (5 points each) Put a circle around the letter that you think is the best answer. I-1 Alice and Tom dive from an overhang into the lake below. Tom simply drops straight down from the edge, but Alice takes a running start and jumps with an initial horizontal velocity of 5 m/s. Neither person experiences any significant air resistance. Just as they reach the lake below A) the speed of Alice is larger than that of Tom. B) the splashdown speed of Alice is larger than that of Tom. C) they will both have the same speed. D) the speed of Tom will always be 9.8 m/s larger than that of Alice. E) the speed of Alice will always be 5 m/s larger than that of Tom. I- Which one of the following free-body diagrams best represents the free-body diagram, with correct relative force magnitudes, of a person in an elevator that is traveling upward but is gradually slowing down at a rate of 9 m/s? f is the force of the floor on the person and g is the force of gravity on the person. A) B) C) D) E)

3 3 Last Name only (PRINT) I-3 A fish weighing 16 N is weighed using two spring scales, each of negligible weight, as shown in the figure. What will be the readings of the scales? A) The bottom scale will read 16 N, and the top scale will read zero. B) Each scale will read 16 N. C) The top scale will read 16 N, and the bottom scale will read zero. D) The scales will have different readings, but the sum of the two readings will be 16 N. E) Each scale will read 8 N. I-4 Two bodies P and Q on a smooth horizontal surface are connected by a light cord. The mass of P is greater than that of Q. A horizontal force (of magnitude F) is applied to Q as shown in the figure, accelerating the bodies to the right. The magnitude of the force exerted by the connecting cord on body P A) will be zero. B) will be less than F but not zero. C) will be equal to F. D) will be greater than F. E) can not be determined relative to F

4 4 Last Name only (PRINT) Part II (30 points) An object with a mass of 175 kg is launched from the ground with a speed of 10 m/s at an angle of 60 degrees above the surface. The object hits a vertical wall which is at a distance of 50 m from the position that the object is launched. A) Draw and label a diagram representing the physical situation. B) Determine the time it takes the object to hit the wall. C) Determine the vertical location on the wall where the object hits. D) Determine the velocity just before the object hits the wall.

5 5 Last Name only (PRINT) Part III (30 points) A block (M A = 30 kg) is on a frictionless horizontal surface and is connected to a second block (M B = 85 kg) which is on an incline with an angle of 5 degrees. The coefficient of kinetic friction between M B and the incline is The two blocks are connected by a massless string that goes over a pulley with M B being below M A. A) Draw and label a diagram representing the physical situation. B) Draw and label a free-body diagram for each block.

6 Part III (continued) 6 Last Name only (PRINT) C) Using Newton s Second Law, write down the 4 equations that will allow the determination of the motion of the blocks. D) Solve the equations in order to determine an expression for the acceleration of the blocks in terms of the non-numeric parameters involved in the problem. E) Determine the numerical values for the acceleration of the blocks and the tension in the string.

7 7 Last Name only (PRINT) Part IV (0 points) A block (M A = 1.0 kg) sits on top of a second block (M B =.0 kg). Block A is connected to a vertical wall by a massless horizontal string. Block B is on a horizontal surface and is acted on by a horizontal force of 0 N in the direction away from the wall. The coefficient of kinetic friction at both the upper and lower surfaces of block B is 0.0. A) Draw and label a diagram representing the physical situation. B) Draw and label a free-body diagram for each block. C) Identify (using words and symbols) all of the action-reaction pairs that are present. D) Determine the tension in string that is connected to the top block A. E) Determine the acceleration of the bottom block B.

8 Formulae for Exam # Spring 015 (page 1) 8 Graphical Analysis r vavg = t t = t t a v a avg inst inst f v = t dr = i dv = = r = r r (slope of position versus time) f i (slope of velocity versus time) (slope of position versus time at a specific time) d r (slope of velocity versus time at a specific time) S f = S i + area under velocity versus time for Δt = t f - t i V fs = V is + area under acceleration versus time for Δt = t f - t i Analytical Analysis (for constant linear acceleration) S 1 f = Si + vis + t as t vfs = vis + as t v = v + a S fs is S ( )

9 9 Graphical Analysis Formulae for Exam # Spring 015 (page ) ω a avg avg θ = t (slope of angular position versus time) ω = t (slope of angular velocity versus time) dθ ω inst = (slope of angular position versus time at a specific time) dω α inst = = d θ (slope of angular velocity versus time at a specific time) Ɵ f = Ɵ i + area under angular velocity versus time for Δt = t f - t i ω fs = ω is + area under angular acceleration versus time for Δt = t f - t i Analytical Analysis (for constant angular acceleration) θ 1 f = θi + ωi + t α t ωf = ωi + α t ω = ω + α θ s f i ( ) = rθ v= rω at = ra a r r = ω = v r