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Phys121 Final 2010_Soln

Phys121 Final 2010_Soln - “My#4”...

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Unformatted text preview: “My _ #4” PhysiZl/SIO/Hassam/Final Name: Signature: Seat Number: 1. Closed Book. Only 2 sheets of paper (double sided) allowed 2. Put final answers into the boxes provided. Show essential work next to box. 3. Express all your answers using two significant figures, if needed. 4. Use reverse sides for scratch work. 5. After you finish the exam, write and Sign the Honor Pledge in the box beiow: “I pledge on my honor that 1 have not given or received any unauthorized assistance on this exam” g = 9.8 rn/s2 Newton’s Gravitation Law: F = Gm;rim/(distance)2 2 - 1 1 l 1 .- .- 2 2 — — 5 0 - 0 - 0 _ 0 5 _ _ Max:200 Problem 1 A car travels at constant speed along the curved path shown in the figure below. Five possible vectors are also shown in the figure; the letter E represents the zero vector. Which vector best represents the car's velocity at position 1? Which vector best represents the car's acceleration at position 1? Which vector best represents the car's velocity at position 2? Which vector best represents the car's acceleration at position 2? Which vector best represents the car's veiocity at position 3? Which vector best represents the car's acceleration at position 3? Problem 2 The figure below shows block A sitting on top of block B. A constant force F is exerted on block B, causing block B to accelerate to the right. Block A rides on block B without slipping. Which statement is true? 1. Block B does not exert a friction force on block A. 2. Block B exerts a friction force on block A, directed to the left. (9 Block B exerts a friction force on block A, directed to the right. Problem 3 As a roller coaster car crosses the top weight is the same as its true weight. Diameter loop—the-loop, its apparent u. ' the car's speed at the top? WWW/1g ==’ “W V first/Mg 2mg :in/V VL: 2V? Problem 4 A 1.0 kg wood block is pressed against a vertical wood wall by a 10 N force as shown in the figure. Assume there is a kinetic friction fore , , f wood on wood and that the magnitude of f = 0.3*n *Where n is the normal force. You are told t lock is sliding and accelerating downward. Find the acceleration downward. ‘52 if J4 m? if] : 1006930 mg —- 06,214 ~(Os‘iw 5’0 L? W“ 9 m Q'Blfiiflflasé’fi m [3(Sfim’b): 0: Mt Problem 5 A package of mass m is released from rest at a warehouse loading dock and slides down a 3.0—In-high frictionless chute to a waiting truck. Unfortunately, the truck driver went on a break without having removed the previous package, of mass 2m, from the bottom of the chute (the bottom of the chute is on a horizontal frictionless surface). Suppose the packages make an inelastic collision and stick together. What is their common speed after the collision? . 1 I), : __. - V mgh 1W V: 2.6.3# Liz—‘9'} Problem 6 In collisions between two objects, momentum is always conserved. If, however, the collision is elastic, kinetic energy is also conserved. An object of mass m]: 1 kg is moving to the right at speed 1 m/s. It makes an elastic collision with a stationary ' f mass mg kg. After the collision, both m1 and m 2 are moving, separately, as ollows: 33 m1 is seen to have slowed down — it is still moving to the right but at spe d 1/4 m/s; ' mfs. Find the mass and its eed V. V m/s Problem 7 In trying to explain sateiiite orbits, Newton proposed his Law of Gravitation, ie, any two masses attract with a force F = Gmlmzldz, where dis the separation distance. He then appiied this law to planetary orbits around the Sun and found that the period T and radius R of any planet’s orbit around the Sun are related according to T2 = (constant)*R3. Suppose instead of the Law given above, he had tried the law F = Gm1m2/d4. What would he have found for the relationship between T and R? Problem 8 The temperature of the air in a basketball increases as it is pumped up. Which one is true? 1. The totai kinetic energy of the air is decreasing and the average kinetic energy of each atom is decreasing. 2. The total kinetic energy of the air is decreasing and the average kinetic energy of each atom is increasing 3. The total kinetic energy of the air is increasing and the average kinetic energy of r _ each atom is decreasing. @ The total kinetic energy of the air is increasing and the average kinetic energy of each atom is increasing. Problem 9 An ideal gas is held in a container of voiume V at pressure P. The rms speed of a gas atom under these conditions is v. If new the volume and pressure are changed to 2V and 2?, the rms speed of the atom will be @2. 2. 4v 3. v/4 4. W2 5. v Problem 10 Two blocks of copper, 1.00kg and 3.00kg, are at the same temperature. 1. Which block has more thermal energy? L49 2. If the blocks are placed in thermal contact, will the thermal energy of the blocks change? If so, how? No Problem 11 Refrigerators have a thermodynamic limit on their COP, given by COP < Tc/(Tt1 _ Tc), where TC(K) is the temperature of the fridge, Th(K) is the environment temperature, and COP is defined as COP *—‘ (heat extracted from fridge)/ (input work). (I) the heat in Joules extracted fi'om the fridge per cycle (2) the heat exhausted to the environment per cycle Problem 12 A 750g aluminum pan is removed from the stove and plunged i a sink fill d with 10.0kg of water at 200°C. The water temperature quickly rises o 30.0°C. What was the initial temperature of the pan? TABLE 12.4 Specific heats of solids and liquids Substance c (Jlkg - K) Solids Lead 128 i I " é -, Gold 129 é C Copper 385 Iron ‘ 44 _ Aluminum 90-0 Water ice 2090 Mammalian bedy 3400 Liquids Mercury [40 Ethyl alcnhol 2400 I W thzflafl Penman swam inc" pubishmq ska-son Mum-mm ...
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