HW #3-4-solutions

# HW #3-4-solutions - pasha(sep635 – HW 3-4 – Antoniewicz...

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Unformatted text preview: pasha (sep635) – HW 3-4 – Antoniewicz – (56445) 1 This print-out should have 28 questions. Multiple-choice questions may continue on the next column or page – find all choices before answering. 001 8.0 points A bullet of mass m traveling horizontally at a very high speed v embeds itself in a block of mass M that is sitting at rest on a nearly frictionless surface. What is the final speed v f of the block-bullet system after the bullet embeds itself in the block? 1. v f = m 2 m + M v 2. v f = m m + M v correct 3. v f = M m v 4. v f = M m + M v 5. v f = m M v Explanation: Assume the bullet travels in the + x direc- tion, so that v bullet , i = h v, , i m / s . Define the system to be the bullet and the block. Assume that the net external force on the system is zero. Apply the momentum principle with the initial momentum being before the collision and the final momentum being after the collision. ~ p bullet , i + ~ p block , i = ~ p bullet , f + ~ p block , f m ~ v bullet , i + 0 = m ~ v f + M ~ v f m ~ v bullet , i + 0 = ( m + M ) ~ v f ⇒ ~ v f = m m + M ~ v bullet , i ⇒ ~ v f = m m + M ~ v bullet , i = m m + M v . 002 (part 1 of 2) 4.0 points A car of mass 2600 kg collides with a truck of mass 4300 kg, and just after the collision the car and truck slide along, stuck together. The car’s velocity just before the collision was ~ v car , i = h 39 , , i m / s , and the truck’s velocity just before the colli- sion was ~ v truck , i = h- 15 , , 29 i m / s . The velocity of the stuck together car and truck just after the collision will be of the form ~ v sys , f = h v sys , f ,x , , v sys , f ,z i m / s . Find the x component, v sys , f ,x . Correct answer: 5 . 34783 kg · m / s. Explanation: We can use the momentum principle. We know that the momenta before and after the collision will be given by ~ p sys , i = m car ~ v car , i + m truck ~ v truck , i ~ p sys , f = ( m car + m truck ) ~ v sys , f The momentum principle predicts that ~ p sys , i = ~ p sys , f , so we can use this to solve for ~ v sys , f . ~ p sys , f = ( m car + m truck ) ~ v sys , f ⇒ ~ v sys , f = ~ p sys , i m car + m truck = m car ~ v car , i + m truck ~ v truck , i m car + m truck = h 5 . 34783 , , 18 . 0725 i kg · m / s . 003 (part 2 of 2) 4.0 points Find the z component, v sys , f ,z . Correct answer: 18 . 0725 kg · m / s. Explanation: See the explanation for part 1. pasha (sep635) – HW 3-4 – Antoniewicz – (56445) 2 004 (part 1 of 7) 2.0 points Object A has mass m A = 8 kg and initial momentum ~ p A,i = h 19 ,- 7 , i kg · m / s , just before it strikes object B, which has mass m B = 11 kg. Just before the collision, object B has initial momentum ~ p B,i = h 7 , 9 , i kg · m / s ....
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## This note was uploaded on 11/17/2011 for the course PHY 303K taught by Professor Turner during the Fall '08 term at University of Texas.

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HW #3-4-solutions - pasha(sep635 – HW 3-4 – Antoniewicz...

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