PracticeExam3Solution-EP1-S08

PracticeExam3Solution-EP1-S08 - Engineering Physics 1...

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22 Engineering Physics 1 (Phys. 213) Practice Exam Solution 3, Mar. 14 th , 2008 (O’Shea) Name __________________________________ Instructions: Please Read! This is a closed book, closed notes exam. This exam contains multiple-choice questions and problems. For each multiple-choice question, circle the letter of the best response. For problems, you need to show your work in a professional manner and write the final numerical answer with the proper unit in the space shown. Numerical answers without supporting calculations will receive zero credit. Partial credit is available only if your work is clear. 1. Academic honesty statement. This exam will NOT be marked unless you sign the academic honesty statement below. Your signature indicates that you have read , understood , and complied with the meaning of this statement. On my honor as a student I have neither given nor received unauthorized aid on this assignment. Sign your name:__________________________________________________________ 2. (1 point) Circle your Studio instructor/hour: Lynch /TU 9:30 Matloob /TU 11:30 Regehr /TU 1:30 O’Shea/WF 7:30 Lynch /WF 9:30 Page total: /1
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23 3. A 3.5 kg block is accelerated from rest by a spring that was compressed by an amount 0.46 m. After the block leaves the spring it then travels over a horizontal floor with a coefficient of kinetic friction k μ = 0.25. The frictional force stops the block in distance D = 7.8 m. a) What is the spring constant? () D f kx W U K k f = + = Δ + Δ 2 2 1 0 0 0 Now mg F f k N k k μ = = Substituting for f k N/m 632 2 2 1 2 2 = = = x mgD k mgD kx k k b) After the mass leaves the spring it will have some initial speed v . How far on the frictional surface has the block traveled when its speed is v /2? Applying conservation of energy with: Initial state = mass compressed against spring Final state = mass just left spring and has speed v m k x v kmv kx / 2 2 1 2 2 1 = = Now apply conservation of energy with: Initial state = mass compressed against spring Final state = mass on friction surface and has speed v /2 ( ) ( ) ( ) m 8 . 5 4 0 0 2 / / 0 0 2 / 2 1 1 2 8 3 1 2 2 1 2 2 1 1 2 2 1 2 2 1 = = = = + = + = Δ + Δ mg kx D mgD kx mgD kx m k x m D f kx v m W U K k k k k f 4. A 500 kg automobile is at rest at a traffic signal.
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PracticeExam3Solution-EP1-S08 - Engineering Physics 1...

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