Second Exam for Physics 102, Section 1, Fall /19/2005

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1 Second Exam for Physics 102, Section 1, Fall /19/2005 Notes: 1) Always assume g=10 m/s 2 for the gravitational acceleration on the Earth s surface. 2) Formulas: a. the distance that is traveled by something that has a constant acceleration when it starts from zero 1 2 velocity: d = at. 2 b. for circular motion, the centripetal acceleration is (v t ) 2 /r, where v t is the tangential velocity and r is the radius 1. A ball is thrown up into the air. What is the acceleration of the ball at the top of its trajectory? A) 0 m/s 2 B) 10 m/s 2 upward C) 10 m/s 2 downward D) 100 m/s 2 upward E) 100 m/s 2 downward F) 1000 m/s 2 downward 2. A car of mass 1000 kg is driven into a repair shop. How much does this car weigh? A) 0 N B) 1 N C) 10 N D) 100 N E) 1000 N F) 10,000 N G) 100,000 N H) 1,000,000 N I) none of the above choices are correct 3. A car that weighs 20,000 N is on the hoist in a repair shop. How much work must be done to lift the car 2 meters? A) 0 J B) 1,000 J C) 2,000 J D) 4,000 J E) 10,000 J F) 20,000 J G) 40,000 J H) none of the above choices are correct 4. How much gravitational potential energy would the car in the previous question acquire if it were lifted 1 meter? A) 0 J B) 1,000 J C) 2,000 J D) 4,000 J E) 10,000 J F) 20,000 J G) 40,000 J H) none of the above choices are correct 5. A person carries a 50N bowling ball so that the ball is moving horizontally at constant velocity. How much work is the person doing on the ball, for each meter that the ball is carried? A) 0 J B) 50 J C) 100 J D) 500 J E) 1,000 J F) 5,000 J 6. A ball is thrown straight up in the air. Where is the kinetic energy maximal? Where is the potential energy maximal? A) KE maximal at the highest point, PE maximal at the lowest point B) KE maximal at the lowest point, PE maximal at the highest point C) Both KE and PE maximal at the lowest point D) Both KE and PE maximal at the highest point

2 7. You are pushing a box across the floor. You are applying 100 N of force to the box. If you can push the box 10 meters in 2 seconds, how much power are you applying to the box? A) 0 W B) 100 W C) 250 W D) 500 W E) 1,000 W F) 2,500 W 8. The force of friction on the box in the above problem has magnitude 50 N. You are applying 100 N of force to the box. If you can push the box 10 meters in 2 seconds, how much of the power you are supplying is going into heat? A) 0 W B) 50 W C) 100 W D) 250 W E) 500 W F) 1,000 W G) 2,500 W H) none of the above choices are correct 11. A sandbag in outer space is moving at 3 m/s. It collides with and sticks to another sandbag which has the same mass but was initially at rest. Compared to the kinetic energy of the moving bag before the collision, the kinetic energy of the coupled bags after the collision is A) zero B) the same C) half as much D) one-third as much E) one-quarter as much F) one-eighth as much 12. A big rubber ball of mass 1 kg is held 2 meters above a hard floor. The ball is dropped, and it only bounces back up to 1.5 meters. How much energy was converted to heat? A) zero B) 0.1 J C) 0.2 J Correct answer is 5J D) 0.5 J E) 1 J F) 2 J 9. A person standing next to a see-saw holds the seesaw so that it is horizontal. The person applies an upward force 2 meters away from the pivot. The person is strong enough to apply up to 100 N of upward force. A bag of cement is hanging from the same side of the see-saw at a point 0.2 meter away from the pivot. What is the maximum weight the bag can have if the person can lift it? A) 0 N B) 1,000 N C) 2,000 N D) 5,000 N E) 10,000 N F) 20,000 N 10. In the previous question, if the pivot is frictionless, which statement is true when the person lifts the bag a small distance? A) The work done by the person equals the work done on the bag B) The work done by the person is greater than the work done on the bag C) The work done by the person is less than the work done on the bag 13. A monster truck has tires with a diameter of 2 meters (about 6 feet!). How fast does the truck go if the wheels rotate at 2.5 revolutions per second? A) zero B) 2.5 m/s C) 5.0 m/s D) 7.85 m/s E) 8.1 m/s F) 15.7 m/s 14. A car is going at a steady speed around a circular track. The net force on the car is A) zero B) toward the center of the track C) along the direction of the car s velocity D) away from the center of the track E) opposite the direction of the car s velocity

3 15. A space habitat of diameter 100 meters rotates to provide simulated lunar gravity, which is 1/6 of the Earth s gravity. At the same rotational speed, what would the diameter need to be to provide 1 Earth gravity? A) 150 meters B) 200 meters C) 300 meters D) 400 meters E) 500 meters F) 600 meters 16. In this sketch, the force F is applied to an object at the position indicated by the black circle. What is the torque created by this force about the point indicated by the star? F a A) F Nm B) F%a Nm C) F%b Nm D) F%c Nm 17. A fulcrum is placed underneath a meter stick so that it pivots at the 50 cm mark. A 50 N mass hangs from the 30 cm mark and a 100 N mass hangs from the 70 cm mark. What is the net torque about the pivot point? A) 0 Nm B) 1 Nm Net torque is 10 Nm C) 2 Nm D) 3 Nm E) 4 Nm F) 5 Nm c b 18. A ring and a disk start rolling down a hill at the same time. Which one reaches the bottom first? A) both arrive at the same time B) the ring C) the disk D) depends on the masses E) not enough information is given 19. The planet Jupiter is a big rotating ball of gas. If Jupiter cooled to the point where the gas all liquefied, Jupiter s rate of rotation about its axis would A) increase B) decrease C) stay the same D) depends on the type of gas 20. If the Earth s radius was reduced to 1/3 its present value while the Earth s mass stayed the same, what would the new value be for gravitational acceleration at the surface of the earth? A) the same, 10 m/s 2 B) 10/3 m/s 2 C) 30 m/s 2 D) 10/6 m/s 2 E) 60 m/s 2 F) 10/9 m/s 2 G) 90 m/s 2 H) none of the above choices are correct 21. In the previous question, what would happen to a satellite that was in a circular orbit around the Earth before the shrinkage? nothing at all would happen to it! A) orbit radius decreases to 1/3 original value B) orbit radius increases to 3X original value C) orbit radius decreases to 1/6 original value D) orbit radius increases to 6X original value E) orbit radius decreases to 1/9 original value F) orbit radius increases to 9X original value 22. We see pictures of astronauts in the space station bouncing around from wall to wall because they are weightless. Why are they weightless.? A) they are in free fall B) they are above the force of the Earth s gravity C) there is no net force of gravity on them

4 23. The Earth s gravity has an attractive force on the Moon, and the Moon s gravity has an attractive force on the Earth. Which statement is true about these two forces? A) the force on the moon is bigger B) the force on the Earth is bigger C) the forces are the same size 24. Consider the Earth and the Sun. If the masses of both were doubled, and the distance between them were doubled, the gravitational force between them would be A) one-quarter as large B) half as large C) twice as large D) four times as large 25. If the Earth was hollowed out in the middle so that all the material from the center of the Earth to 1/2 the Earth s radius was gone, and you let go of a rock at the new inner surface of the Earth at 1/2 the Earth s radius, the gravitational acceleration of the rock would be A) 0 B) 1/4 g C) 1/2 g D) g E) 2 g F) 4 g 27. Jupiter s orbit is about 5 times farther from the Sun than the Earth s orbit. According to Newton s Universal Law of Gravitation, what is the gravitational acceleration due to the Sun at the orbit of Jupiter compared to its value at the orbit of the Earth? A) 25 times smaller B) 5 times smaller C) the same D) 5 times bigger E) 25 times bigger 28. A man standing on a platform throws a ball horizontally. The ball s height when it leaves his hand is 20 meters. How much time passes before the ball hits the ground? A) depends on how fast the ball was thrown B) depends on how far the ball was thrown C) 1 second D) 2 seconds E) 3 seconds 29. In general, orbits are elliptical (this was first discovered by Kepler) circular orbits are a special case. Where in the elliptical orbit is the satellite s acceleration the largest? 26. What is the force of gravity on a 500-newton person standing on the Earth s surface? A) 50 N B) 250 N C) 500 N D) 5000 N E) need more information to say A) B) C) D) E) all the same

5 30. Where in the elliptical orbit is the satellite s potential energy the largest? 32. Where in the elliptical orbit is the satellite s angular momentum about the center of the Earth the largest? A) B) C) D) E) all the same A) B) C) D) E) all the same 31. Where in the elliptical orbit is the satellite s kinetic energy the largest? 33. For a satellite in circular orbit, as the altitude of the satellite increases the orbital period of the satellite A) decreases B) remains unchanged C) increases D) need more information A) B) C) D) E) all the same 34. Which of the following is not a vector quantity? A) acceleration B) velocity C) kinetic energy D) momentum E) force F) all of them are vector quantities 35. A ball is thrown at a 45-degree angle above horizontal. Neglecting air drag, as the ball rises its A) horizontal velocity decreases and its vertical velocity increases B) horizontal velocity decreases and its vertical velocity decreases C) horizontal velocity stays the same and its vertical velocity increases D) horizontal velocity stays the same and its vertical velocity decreases E) horizontal velocity increases and its vertical velocity decreases F) horizontal velocity increases and its vertical velocity increases

6 36. Which of the following are electrically neutral? A) atoms and protons B) protons and neutrons C) neutrons and electrons D) electrons and atoms E) atoms and neutrons 37. Which of the following was not discovered by J. J. Thomson using cathode-ray tubes? A) electrons are corpuscular B) electrons are negatively charged C) electrons are much less massive than the lightest atom D) electrons are always exactly the same, regardless of what atoms they re emitted from 38. Ernest Rutherford discovered that alpha particles, which are almost as heavy as helium atoms and are positively charged, would usually go through thin metal foils, but every once in a while an alpha particle would bounce almost straight backwards. What new information did this reveal about the structure of the atom? A) that most of the atom s mass is in a compact, positively-charged nucleus B) that most of the atom s mass is in a compact, negatively-charged nucleus C) that electrons are corpuscular and are distributed throughout the atom D) that electrons have negative charge E) that atoms contain neutrons 39. All the atoms in the Earth, and in you (except for the hydrogen and some of the helium) were created billions of years ago in A) interstellar space B) the Sun C) the primordial Earth itself D) stars that exploded E) interplanetary collisions F) the solar wind 40. What kind of force prevents atoms from being squashed together? A) gravitational B) electrical C) magnetic D) strong nuclear force E) weak nuclear force 41. How many protons must there be in an element that has 27 electrons? A) less than 27 B) exactly 27 C) more than 27 D) depends on the number of neutrons present E) need more information 42. Which of these physical theories or ideas did not suggest that atoms exist? A) gravitation B) Brownian motion C) kinetic theory of gases D) Dalton s theory of law of simple and multiple proportions in chemical reactions 43. Assume that the deformation of a solid is taking place within the elastic limit. If 1 N of force produces a deformation of 1 millimeter (mm), how much deformation will be produced by 9 N of force? A) 1/9 mm B) 1/3 mm C) 1 mm D) 3 mm E) 9 mm F) need more information 44. Assume that the deformation of a solid exceeds the elastic limit. If 1 N of force produces a deformation of 1 millimeter (mm), how much deformation will be produced by 9 N of force? A) 1/9 mm B) 1/3 mm C) 1 mm D) 3 mm E) 9 mm F) need more information

7 45. Water expands when it freezes. This tells us A) the density of water is greater than the density of ice B) the density of ice is greater than the density of water C) it doesn t tell us anything about the relative densities of ice and water 46. Archimedes prepares two big cubical samples. Both samples measure 1 m x 1 m x 1 m. One sample is made of Styrofoam and the other one of iron. When the cubes are fully submerged in water (completely under the surface of the water), the buoyant force A) is bigger for the Styrofoam cube B) is bigger for the iron cube C) is the same for both cubes D) need additional information 47. At a depth of 100 meters in water, the pressure is approximately 10 atmospheres (100 N/cm 2 ). An aluminum cube, with each face 10 cm x 10 cm, is accidentally dropped over the side of a ship. When the cube has dropped to 100 meters depth, about how much force does the water exert on one face of the cube? A) 1 N B) 10 N C) 100 N D) 1,000 N E) 10,000 N 48. Assume that the cube in the previous question is hollow. Water masses 1000 kg per cubic meter and is nearly incompressible. What is the biggest the mass of the hollow aluminum cube could be, in order for the cube to float rather than sink? A) less than 0.1 kg B) less than 1 kg C) less than 10 kg D) less than 100 kg E) less than 1000 kg F) need more information 49. Atmospheric pressure is caused by the A) density of the atmosphere B) weight of the atmosphere C) temperature of the atmosphere D) effect of the sun s energy on the atmosphere 50. A balloon is buoyed up with a force equal to the A) weight of air it displaces B) density of the surrounding air C) atmospheric pressure D) weight of the balloon and contents E) all of the above 51. Imagine that you were standing on a weighing scale and all of a sudden the atmosphere vanished. For the brief period that you remained conscious and standing on the scale, you would notice that the reading on the scale had A) increased B) decreased C) remained the same D) need more information 52. Because of the asymmetrical form of the interatomic potential energy curve, when most liquids and solids are heated, their atoms A) move closer together, on average B) move farther apart, on average C) stay the same distance apart, on average D) need more information to answer 53. When you touch a cold piece of ice with your finger, energy flows A) from your finger to the ice B) from the ice to your finger C) actually, both ways D) need more information to answer 54. A substance that heats up more for a given input of energy has a A) high specific heat B) low specific heat C) high conductivity D) low conductivity E) need more information to answer

8 55. When a metal ring is heated, the hole in the ring becomes A) larger B) smaller C) stays the same size D) depends on the ring dimensions 60. What color should a motorcycle engine be to obtain maximum cooling of the engine by radiation? A) white B) black C) red D) chrome-plated 56. Lake Superior is a deep lake that ices over in the winters. What s the temperature at the bottom of Lake Superior in the middle of the winter? A) below 0C B) 0C C) between 0C and 4C D) 4C E) above 4C 57. Pour a liter of water at 40 degrees C into a liter of water at 20 degrees C and the final temperature of the two becomes A) less than 30 degrees C B) at or about 30 degrees C C) more than 30 degrees C 58. A closed, sealed can of air is placed on a hot stove. The contained air undergoes an increase in A) mass B) pressure C) temperature D) all of these E) two of these 59. The Sun shines down on the ocean coastline. The land heats up to a higher temperature than the water, and the warm air over the land starts to rise. Cooler ocean air flows onto the coast in an onshore breeze. The heat transfer by the air is best described as A) conduction B) convection C) radiation

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