Problem 1: Which statement is correct?

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Daniela Sherman
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Problems 1-2 A water molecule contains one oxygen (O) and two hydrogen (H) atoms. There is a positive charge of +0.335e on each H and negative charge of -0.670e on the O atom.

1 Problems 1-2 A water molecule contains one oxygen (O) and two hydrogen (H) atoms. There is a positive charge of e on each H and negative charge of e on the O atom. Problem 1: Which statement is correct? A. The force on the O atom by H atoms is larger than the force on H atoms by the O atom B. The force on H atoms by the O atom is larger than the force on the O atom by H atoms C. The forces are equal in magnitude D. The forces are equal E. not enough information is given Problem 2: Calculate the electrostatic potential energy stored in the H 2 O molecule. A) J B) J C) N D) N E) zero Problem 3. During alpha decay Uranium 238 decays into Thorium-234 and an alpha particle (Helium-4). Which of the following statements is correct: A) momentum and total energy are conserved during the decay B) total energy, momentum and mass are conserved during the decay C) kinetic energy and momentum are conserved during the decay D) potential energy is conserved during the decay E) kinetic energy is conserved during the decay

2 Problem 4. In a cathode ray tube (CRT) used in oscilloscopes and television sets, a beam of electrons is steered to different places by electrostatic produced by a plane capacitor. Assume that a force F is applied only while electrons are between the plates and that initial speed v 0 <<c. Neglecting gravitational force, calculate the height y f where electron will hit the screen. A) Fd 2 /mv o 2 B) Fl 2 /m v o 2 C) Fd(d+0.5l)/mv o 2 D) Fd(l+0.5d)/mv o 2 E) Fd(d+l)/mv o 2 Problem 5. An unstable Pu-240 nucleus (mass u) is at rest when it fissions into two Ag-120 nuclei (mass u) which then fly off far from each other. Find the final kinetic energy of one Ag-120 nucleus when it is far from the other one. (1u = 1 atomic mass unit = kg) A) J B) J C) J D) J E) J

3 Problem 6. The figure below is a graph of the energy of a system of a planet interacting with a star. The gravitational potential energy U g is shown as the thick curve, and plotted along the vertical axis are various values of K+U g. Suppose that K+U g of the system is A. Find all of the true statements below. 1. The potential energy of the system decreases as the planet moves from r 1 to r The potential energy of the system increases as the planet moves from r 1 to r When the separation between the two bodies is r 2, the kinetic energy of the system is A-B. 4. The system is a bound system; the planet can never escape. 5. The path traced by this orbiting system is a circle. 6. When the separation between the two bodies is r 1, the kinetic energy of the system is B-C. A) 1,4,5 B) 2,4,5 C) 1,3,4 D) 2,3,4

4 Problem 7. Consider a system of two stars. For this system the gravitational potential energy is maximized when: A. The stars are far away from each other. B. The stars are as close to each other as possible. C. The stars are infinitely far away from each other. D. There is no gravitational potential energy. E. None of the above. Problem 8. Consider a closed system consisting of a star and an asteroid orbiting the star along elliptical orbit. As the asteroid moves around the star its distance to the star and its velocity change. For this system the total energy is largest when: A. the star and asteroid are as far away from each other as possible B. The star and asteroid are as close to each other as possible. C. The asteroid moves at highest speed. D. Both B and C are correct E. None of the above.

5 Problem 10: A boat carrying a large rock is floating on a lake. The rock is thrown overboard and it sinks. Select the correct answer. A. The water level in the lake falls B. The water level in the lake rises C. The water level in the lake remains unchanged D. Need more info to conclude. Problem 11 We drop a coffee filter of mass 1.2 grams from a height of 20 meters. The filter reaches the ground with a speed of 0.4 m/s. How much work was done on the filter by the air molecules? A) J B) J C) J D) J E) 0 J

Problem 12 Joule s paddle wheel experiment consists of a falling weight which spins a paddle-wheel in an insulated barrel of water. As the weight falls, the water warms up.

6 Problem 12 Joule s paddle wheel experiment consists of a falling weight which spins a paddle-wheel in an insulated barrel of water. As the weight falls, the water warms up. Assume idealized conditions with no friction in the pulley, string, and bearings. How much does the temperature of the water change? Assume there is 0.4 kg of water, the weight has m=100 kg and it falls 1 m. The specific heat capacity of water is 4.2 J/g/K. A) 0.19 degrees B) 0.29 degrees C) 1.16 degrees D) 0.58 degrees E) 3.6 degrees Problem 13 A ball of mass m is attached to a string of length R such that it is free to swing in the vertical plane. The ball is released from the initial position A shown in the picture. What is the tension in the string when the ball reaches the lowest point B of its trajectory? A. mg B. 2mg C. 3mg D. mg/r E. mg2/r

7 Problem 14 A ball of mass m falls from a height h to the surface of the Earth. Which one of the following is correct? (assume that h is much smaller than the radius of the Earth) A) If we choose our system to be ball+earth, then the external work done on the system is zero B) If we choose our system to be ball+earth then the external work done on the system is mgh C) If we choose our system to be just the ball, then the external work done on the system is - mgh D) If we choose our system to be just the ball, then the change in the potential energy is - mgh

B) The small number of nuclear decays within the object decreases the rest mass of the falling object.

B) The small number of nuclear decays within the object decreases the rest mass of the falling object. Problem 1. An unstable Pu- 240 nucleus (mass 240.002 u) is at rest when it fissions into two Ag- 120 nuclei (mass 119.893 u) which then fly off far from each other. Find the final kinetic energy of one