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PracticeExam3Solution-EP1-S08

# PracticeExam3Solution-EP1-S08 - Engineering Physics 1(Phys...

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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 μ = = Substituting for f k N/m 632 2 2 1 2 2 = = = x mgD k mgD kx k k μ μ 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 μ μ μ 4. A 500 kg automobile is at rest at a traffic signal.
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PracticeExam3Solution-EP1-S08 - Engineering Physics 1(Phys...

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