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.

Transcription

1 Phys121/S10/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 below: I pledge on my honor that I have not given or received any unauthorized assistance on this exam g = 9.8 m/s 2 Newton s Gravitation Law: F = Gm 1 m 2 /(distance) 2 Problem Max score Score Problem Max score Score Max=200

2 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 velocity 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. 3. Block B exerts a friction force on block A, directed to the right.

3 Problem 3 As a roller coaster car crosses the top of a 80m diameter loop-the-loop, its apparent weight is the same as its true weight. What is the car's speed at the top?

4 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 force, f, for wood on wood and that the magnitude of f = 0.3*n, where n is the normal force. You are told that the block is sliding and accelerating downward. Find the acceleration downward N N

5 Problem 5 A package of mass m is released from rest at a warehouse loading dock and slides down a 3.0-m-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?

6 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 = 1 kg is moving to the right at speed 1 m/s. It makes an elastic collision with a stationary object of mass m 2 kg. After the collision, both m 1 and m 2 are moving, separately, as follows: mass m 1 is seen to have slowed down it is still moving to the right but at speed 1/4 m/s; mass m 2 is seen to be moving to the right, at speed V m/s. Find the mass m 2 and its speed V. m 2 kg V m/s

7 Problem 7 In trying to explain satellite orbits, Newton proposed his Law of Gravitation, ie, any two masses attract with a force F = Gm 1 m 2 /d 2, where d is the separation distance. He then applied 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 T 2 = (constant)*r 3. Suppose instead of the Law given above, he had tried the law F = Gm 1 m 2 /d 5. What would he have found for the relationship between T and R?

8 Problem 8 The temperature of the air in a basketball increases as it is pumped up. Which one is true? 1. The total 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 each atom is decreasing. 4. 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 volume V at pressure P. The rms speed of a gas atom under these conditions is v. If now the volume and pressure are changed to 2V and 2P, the rms speed of the atom will be 1. 2v 2. 4v 3. v/4 4. v/2 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? 2. If the blocks are placed in thermal contact, will the thermal energy of the blocks change? If so, how?

9 Problem 11 Refrigerators have a thermodynamic limit on their COP, given by COP < T c /(T h - T c ), where T c (K) is the temperature of the fridge, T h (K) is the environment temperature, and COP is defined as COP = (heat extracted from fridge)/(input work). A fridge is in an environment which is at 127 degrees C, and we desire to operate the fridge at 27 degrees C. You are provided with a motor that can provide 80J per cycle and a system that is optimized to give a COP equal to ½ of the thermo limit. Find (1) the heat in Joules extracted from the fridge per cycle (2) the heat exhausted to the environment per cycle (1) (2)

10 Problem 12 A 750g aluminum pan is removed from the stove and plunged into a sink filled with 10.0kg of water at 20.0 C. The water temperature quickly rises to 30.0 C. What was the initial temperature of the pan? C