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SELECTED PROBLEMS ON KINEMATICS AND NEWTON'S LAWS 1) A motorist travels for 3.0 h at 80 km/h and 2.0 h at 100 km/h. What is her average speed for the trip? A) 85 km/h B) 88 km/h C) 90 km/h D) 92 km/h Answer: B 2) If you run a complete loop around an outdoor track (400 m), in 100 s, your average velocity is A) 0.25 m/s. B) 4.0 m/s. C) 40,000 m/s. D) zero. Answer: D 3) A car traveling 60 km/h accelerates at the rate of 2 2.0 m/s . How much time is required for the car to reach a speed of 90 km/h? A) 15 s B) 30 s C) 45 s D) 4.2 s Answer: D 4)A cart with an initial velocity of 5.0 m/s experiences 2 a constant acceleration of 2.0 m/s . What is the cart's displacement during the first 6.0 s of its motion? A) 10 m B) 55 m C) 66 m D) 80 m Answer: C 5) An object is thrown upward with a speed of 12 m/s on the surface of planet X where the acceleration due 2 to gravity is 1.5 m/s . What is the maximum height reached by the object? A) 8.0 m B) 18 m C) 48 m D) 144 m Answer: C 6) A ball is thrown upward at a velocity of 19.6 m/s. What is its velocity after 3.00 s? A) 9.8 m/s upward B) 9.8 m/s downward C) zero D) 19.6 downward Answer: B 7) If the acceleration of an object is always directed perpendicular to its velocity, A) the object is speeding up. B) the object is slowing down. C) the object is turning. D) this situation would not be physically possible. Answer: C 8) In the absence of an external force, a moving object will A) stop immediately. B) slow down and eventually come to a stop. C) go faster and faster. D) move with constant velocity. Answer: D 9) You are standing in a moving bus, facing forward, and you suddenly fall forward. You can imply from this that the bus's A) velocity decreased. B) velocity increased. C) speed remained the same, but it's turning to the right. D) speed remained the same, but it's turning to the left. Answer: A 10)An object is initially located at the origin has an 2 acceleration of a = 2 j m/s and an initial velocity of vi = 3 i m/s. Find the magnitude of the velocity of the object at t = 2 seconds. A) 5 m/s. B) 7.8 m/s. C) 5.8 m/s. D) 25 m/s. Answer: A 3 11)The position of an object is given by x = 2t , where x is measured in meters and t is measured in seconds. What is the average velocity of the object between t = 1 s and t = 3 s? A) 185 m/s. B) 26 m/s. C) 30 m/s. D) 28m/s. Answer: B 12)A particle moves on a circular path according to 3 the relation θ(t) = 2 t -t where t is in seconds and θ is in radians. What is the angular velocity of the particle at t = 10 seconds?. A) 600 rad/s B) 599 rad/s C)1999 rad/s D)119 rad/s Answer: A 13) A net force F acts on a mass m and produces an acceleration a. What acceleration results if a net force 2F acts on mass 4m? A) a/2 B) 8a C) 4a D) 2a Answer: D 14) If you blow up a balloon, and then release it, the balloon will fly away. This is an illustration of A) Newton's first law. B) Newton's second law. C) Newton's third law. D) Galileo's law of inertia. Answer: C 15) A 20-N weight and a 5.0-N weight are dropped simultaneously from the same height. Ignore air resistance. Compare their accelerations. A) The 20 N weight accelerates faster because it is heavier. B) The 20 N weight accelerates faster because it has more inertia. C) The 5.0 N weight accelerates faster because it has a smaller mass. D) They both accelerate at the same rate because they have the same weight to mass ratio. Answer: D 16) An object of mass m is hanging by a string from the ceiling of an elevator. The elevator is moving upward, but slowing down. What is the tension in the string? A) less than mg B) exactly mg C) greater than mg D) zero Answer: A 23) A wheel accelerates with a constant angular 2 acceleration of 4.5 rad/s . If the initial angular velocity is 1.0 rad/s, what is the angle the wheel rotates through in 2.0 s? A) 11 rad B) 9.0 rad C) 7.0 rad D) 4.5 rad Answer: A 17) A person on a scale rides in an elevator. If the mass of the person is 60.0 kg and the elevator accelerates downward with an acceleration of 4.90 m/s2, what is the reading on the scale? A) 147 N B) 294 N C) 588 N D) 882 N Answer: B 24) A wheel accelerates with a constant angular 2 acceleration of 4.5 rad/s . If the initial angular velocity is 1.0 rad/s, what is the angular velocity at t = 2.0 s? A) 1.0 rad/s B) 7.0 rad/s C) 9.0 rad/s D) 10 rad/s Answer: D 18) A student pulls a box of books on a smooth horizontal floor with a force of 100 N in a direction of 37e above the horizontal. If the mass of the box and the books is 40.0 kg, what is the acceleration of the box? 2 A) 1.5 m/s 2 B) 1.9 m/s 2 C) 2.0 m/s 2 D) 3.3 m/s Answer: C 25) A wheel of diameter of 68.0 cm slows down uniformly from 8.40 m/s to rest over a distance of 115 m. What is the total number of revolutions the wheel rotates in coming to rest? A) 53.8 rev B) 26.9 rev C) 338 rev D) 169 rev Answer: A 19) A traffic light of weight 100 N is supported by two ropes as shown in the Fig. What are the tensions in the ropes? A) 50 N B) 63 N C) 66 N D) 83 N Answer: D 20) Two boxes of masses m and 2m are in contact with each other on a frictionless surface. (SeeFig.) What is the acceleration of the more massive box? A) F/m B) F/(2m) C) F/(3m) D) F/(4m) Answer: C 21) Consider a particle moving with constant speed such that its acceleration of constant magnitude is always perpendicular to its velocity. A) It is moving in a straight line. B) It is moving in a circle. C) It is moving in a parabola. D) None of the above is definitely true all of the time. Answer: B 22) 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) zero 2 B) 0.17 m/s 2 C) 5.0 m/s 2 D) 6.0 m/s Answer: D 26) In the Atwood machine shown in the Fig, if M = 0.60 kg and m = 0.40 kg, what is the magnitude of the acceleration of the system? (Ignore friction and the mass of the pulley.) 2 A) 5.3 m/s 2 B) 3.9 m/s 2 C) 2.0 m/s 2 D) 0.98 m/s Answer: C __________________________________________ __________________________________________ __________________________________________ ____