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Unformatted text preview: markowitz (am45362) – Practice Questions for Exam 2 – distler – (56295) 1 This printout should have 11 questions. Multiplechoice questions may continue on the next column or page – find all choices before answering. 001 10.0 points A 4 . 3 g bullet is stopped in a block of wood ( m w = 4 . 8 kg). The speed of the bullet pluswood combination immediately after the collision is 0 . 71 m / s. What was the original speed of the bullet? Correct answer: 793 . 268 m / s. Explanation: The final momentum of the bulletplus wood system is p f = ( m bu + m w ) v c This must also equal the initial momentum of the system p i = p f Since the wood block is initially at rest, the only momentum contribution is from the bul let p i = m bu v b Solving for v b and substituting in from above gives v b = m bu + m w m bu v c = ( . 0043 kg + 4 . 8 kg . 0043 kg ) (0 . 71 m / s) = 793 . 268 m / s 002 10.0 points Particle 1 with momentum → p 1 strikes Par ticle 2, which is at rest. The particles move in different directions after the collision. The momenta after the collision are → p 1 ′ and → p 2 ′ . What relationship is true? 1. p 1 x = p ′ 1 x − p ′ 2 x 2. p 1 y = p ′ 1 y − p ′ 2 y 3. p 1 y = p ′ 2 y 4. p 1 x = p ′ 1 x + p ′ 2 x correct 5. ( p ′ 1 ) 2 = p 2 1 + ( p ′ 2 ) 2 6. → p 1 ′ = → p 2 ′ 7. p 2 1 = ( p ′ 1 ) 2 + ( p ′ 2 ) 2 Explanation: The momentum is conserved. We have → p 1 = → p 1 ′ + → p 2 ′ So in the x direction, p 1 x = p ′ 1 x + p ′ 2 x , and in the y direction, p 1 y = p ′ 1 y + p ′ 2 y . 003 10.0 points A rock of mass m is thrown horizontally off a building from a height h . The speed of the rock as it leaves the thrower’s hand at the edge of the building is v , as shown. m h v m What is the kinetic energy of the rock just before it hits the ground? 1. K f = 1 2 mv 2 + mg h correct 2. K f = 1 2 mv 2 3. K f = 1 2 mv 2 − mg h 4. K f = mg h − 1 2 mv 2 5. K f = mg h Explanation: We can use workenergy theorem, K f − K i = W , where in the present problem, W = ( mg ) h , and K i = 1 2 mv 2 ....
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This note was uploaded on 11/29/2011 for the course PHY 302K taught by Professor Kaplunovsky during the Spring '08 term at University of Texas at Austin.
 Spring '08
 Kaplunovsky
 Physics

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