Exam #2, Chapters 5-7 Name PHYS 101-4M MULTIPLE CHOICE. Choose the one alternative that best completes the statement or answers the question. 1) The quantity 1/2 mv2 is A) the potential energy of the object. B) the work done on the object by the force. C) the power supplied to the object by the force. D) the kinetic energy of the object. 2) The quantity 1/2 kx2 is A) the elastic potential energy of the object. B) the work done on the object by the force. C) the power supplied to the object by the force. D) the kinetic energy of the object. 3) The quantity mgy is A) the work done on the object by the force. B) the power supplied to the object by the force. C) the gravitational potential energy of the object. D) the kinetic energy of the object. 4) Is it possible for the kinetic energy of an object to be negative? A) yes B) no 5) Compared to its mass on the Earth, the mass of an object on the Moon is A) less. B) half as much. C) more. D) the same. 6) Two stones, one twice the mass of the other, are dropped from a cliff. Just before hitting the ground, what is the kinetic energy of the heavy stone compared to the light one? A) twice as much B) half as much C) the same D) quarter as much E) four times as much 7) An open cart rolls along a frictionless track while it is raining. As it rolls, what happens to the speed of the cart as the rain collects in it? (assume that the rain falls vertically into the box) A) slows down B) speeds up C) stops immediately D) maintains constant speed 8) Is it possible for an object moving with a constant speed to accelerate? Explain. A) Yes, if an object is moving it can experience acceleration B) No, an object can accelerate only if there is a net force acting on it. C) Yes, although the speed is constant, the direction of the velocity can be changing. D) No, if the speed is constant then the acceleration is equal to zero. 1) 2) 3) 4) 5) 6) 7) 8) 1
9) The mass of the Moon is 7.4 1022 kg and its mean radius is 1.75 103 km. What is the acceleration due to gravity at the surface of the Moon? (G=6.67x10-11 N m2/kg2) A) 1.6 m/s2 B) 2.8 106 m/s2 C) 0.80 m/s2 D) 9.80 m/s2 9) 10) An object moves with a constant speed of 30 m/s on a circular track of radius 150 m. What is the acceleration of the object? A) 5.0 m/s2 B) zero C) 0.17 m/s2 D) 6.0 m/s2 10) 11) Two objects attract each other gravitationally. If the distance between their centers is cut in half, the gravitational force 11) A) is cut to one fourth. B) is cut in half. C) quadruples D) doubles. 12) As a rocket moves away from the Earth's surface, the rocket's weight A) increases. B) depends on how fast it is moving. C) decreases. D) remains the same. 12) 13) When an object experiences uniform circular motion, the direction of the acceleration is A) in the same direction as the velocity vector. B) is directed away from the center of the circular path. C) in the opposite direction of the velocity vector. D) is directed toward the center of the circular path. 13) 14) When an object experiences uniform circular motion, the direction of the net force is A) in the opposite direction of the motion of the object. B) in the same direction as the motion of the object. C) is directed away from the center of the circular path. D) is directed toward the center of the circular path. 14) 15) A spring is characterized by a spring constant of 60 N/m. How much potential energy does it store, when stretched by 1.0 cm? 15) A) 0.30 J B) 600 J C) 3.0 10-3 J D) 60 J 16) A 60-kg skier starts from rest from the top of a 50-m high slope. What is the speed of the skier on reaching the bottom of the slope? (Neglect friction.) 16) A) 9.8 m/s B) 31 m/s C) 41 m/s D) 22 m/s 17) A 10-kg mass, hung onto a spring, causes the spring to stretch 2.0 cm. What is the spring constant? A) 4.9 103 N/m B) 2.0 N/m C) 20 N/m D) 9.0 103 N/m 17) 18) A horizontal force of 200 N is applied to move a 55-kg cart (initially at rest) across a 10 m level surface. What is the final kinetic energy of the cart? 18) A) 4.0 103 J B) 2.7 103 J C) 1.0 103 J D) 2.0 103 J 2
19) A horizontal force of 200 N is applied to move a 55-kg cart (initially at rest) across a 10 m level surface. What is the final speed of the cart? 19) A) 8.5 m/s B) 73 m/s C) 6.0 m/s D) 36 m/s 20) A 500-kg elevator is pulled upward with a constant force of 5500 N for a distance of 50.0 m. What is the work done by the 5500 N force? 20) A) -5.20 105 J B) -2.45 105 J C) 3.00 104 J D) 2.75 105 J 21) An object is lifted vertically 2.0 m and held there. If the object weighs 90 N, how much work was done in lifting it? 21) A) 360 J B) 180 J C) 0 J D) 90 J 22) An acorn falls from a tree. Compare its kinetic energy K, to its potential energy U. A) K increases and U decreases. B) K decreases and U increases. C) K increases and U increases. D) K decreases and U decreases. 22) 23) If the net work done on an object is positive, then the object's kinetic energy A) decreases. B) is zero. C) increases. D) remains the same. 23) 24) What is the correct unit of work expressed in SI units? A) kg m2/s B) kg m2/s2 C) kg m/s2 D) kg2 m/s2 24) 25) A 70-kg astronaut is space-walking outside the space capsule and is stationary when the tether line breaks. As a means of returning to the capsule he throws his 2.0-kg space hammer at a speed of 14 m/s away from the capsule. At what speed does the astronaut move toward the capsule? 25) A) 5.0 m/s B) 0.40 m/s C) 1.5 m/s D) 3.5 m/s 26) What is the momentum of a 2000-kg truck traveling at 35 m/s? A) 3.5 104 kgœm/s B) 7.0 105 kgœm/s C) 7.0 104 kgœm/s D) 57 kgœm/s 26) 27) A 1200-kg ferryboat is moving south at 20 m/s. What is the magnitude of its momentum? A) 2.4 104 kgœm/s B) 6.0 102 kgœm/s C) 1.7 10-3 kgœm/s D) 2.4 103 kgœm/s 27) 28) When a cannon fires a cannonball, the cannon will recoil backward because the A) momentum of the cannonball and cannon is conserved. B) energy of the cannonball and cannon is conserved. C) momentum of the cannon is greater than the energy of the cannonball. D) energy of the cannon is greater than the energy of the cannonball. 28) 29) You're on a ferris wheel moving in a vertical circle. When the ferris wheel is at rest, the normal force N exerted by your seat is equal to your weight mg. How does N change at the top of the ferris wheel when you are in motion? 29) A) N remains equal to mg B) N is larger than mg C) N is smaller than mg D) None of the above 3
30) You weigh yourself on a scale inside an airplane that is flying with constant speed at an altitude of 20,000 feet. How does your measured weight in the airplane compare with your weight as measured on the surface of the Earth? A) greater than B) less than C) same 31) In a baseball game, the catcher stops a 90-mph pitch. What can you say about the work done by the catcher on the ball? A) catcher has done negative work B) catcher has done zero work C) catcher has done positive work 32) An object moves in a circular path at a constant speed. Compare the direction of the object's velocity and acceleration vectors. A) The vectors are perpendicular. B) The vectors point in opposite directions. C) Both vectors point in the same direction. D) The question is meaningless, since the acceleration is zero. 33) A car goes around a flat curve of radius 50 m at a speed of 14 m/s. What must be the minimum coefficient of friction between the tires and the road for the car to make the turn? A) 0.80 B) 0.60 C) 0.20 D) 0.40 34) A 0.50-kg mass is attached to the end of a 1.0-m string. The system is whirled in a horizontal circular path. If the maximum tension that the string can withstand is 350 N. What is the maximum speed of the mass if the string is not to break? A) 13 m/s B) 19 m/s C) 700 m/s D) 26 m/s 35) A motorcycle has a mass of 250 kg. It goes around a 13.7 m radius turn at 96.5 km/h. What is the centripetal force on the motorcycle? A) 2.95 103 N B) 1.31 104 N C) 719 N D) 4.31 104 N 36) A car goes around a curve of radius r at a constant speed v. What is the direction of the net force on the car? A) toward the front of the car B) away from the curve's center C) toward the curve's center D) toward the back of the car 30) 31) 32) 33) 34) 35) 36) 4
FIGURE 6-2 37) A roller coaster starts from rest at a point 45 m above the bottom of a dip (See Fig. 6-2). Neglect friction, what will be the speed of the roller coaster at the top of the next slope, which is 30 m above the bottom of the dip? A) 30 m/s B) 14 m/s C) 24 m/s D) 17 m/s 38) An object slides down a frictionless inclined plane. At the bottom, it has a speed of 9.80 m/s. What is the vertical height of the plane? A) 4.90 m B) 9.80 m C) 19.6 m D) 2.45 m 39) Does the centripetal force acting on an object do work on the object? A) No, because the object has constant speed. B) No, because the force and the displacement of the object are perpendicular. C) Yes, since a force acts and the object moves, and work is force times distance. D) Yes, since it takes energy to turn an object. 40) A 3.0-kg object moves to the right at 4.0 m/s. It collides head-on with a 6.0-kg object moving to the left at 2.0 m/s. Which statement is correct? A) The total momentum both before and after the collision is zero. B) The total momentum both before and after the collision is 24 kgœm/s. C) The total momentum before the collision is 24 kgœm/s, and after the collision is 0 kgœm/s. D) None of the above is true. 37) 38) 39) 40) 5
Answer Key Testname: EXAM2 1) D 2) A 3) C 4) B 5) D 6) A 7) A 8) C 9) A 10) D 11) C 12) C 13) D 14) D 15) C 16) B 17) A 18) D 19) A 20) D 21) B 22) A 23) C 24) B 25) B 26) C 27) A 28) A 29) B 30) B 31) A 32) A 33) D 34) D 35) B 36) C 37) D 38) A 39) B 40) A 6