Physics Chapter 12  Newton's Laws of Motion  Quiz Questions (#1 #7)

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Q11: State and give an example of Newton's 1st Law of Motion. 
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A11: An object at rest remains at rest and an object in motion maintains its velocity unless it experiences a net force. A ball rolling across a table will continue until an outside force acts upon it. 
Q12: Explain the concept of "net force." 
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A12: A net force is the sum of all forces acting on an object. A net force is capable of accelerating a mass. 
Q13: Define the word "inertia." 
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A13: Inertia is the tendency of an object to resist a change in motion unless an outside force acts on the object. 
Q14: How is inertia related to mass? 
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A14: The more mass an object has, the more inertia it has. 
Q15: A magician pulls a table cloth out from underneath a set of dishes without moving or breaking the dishes. Using Newton's 1st Law, explain how this is possible. 
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A15: The dishes stay on the table because of inertia. They resist a change in motion. 
Q16: When you are a rider in a car and the driver makes a sharp turn, you appear to slide towards the side of the car. Use Newton's 1st Law to explain this. 
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A16: You continue moving in the direction you were going before the car turned. Because of inertia, your body resists the change in direction. 
Q17: Why are babies placed in backwardsfacing car seats? 
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A17: The force that is needed to bring the baby to a stop is safely spread out over the baby's whole body. If the baby was only restrained by a seat belt, upon collison the seat belt would cause internal injuries. 
Q18: Why do passengers wear seat belts? 
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A18: Without a seat belt in a crash, the car would slow down quickly, but you would not. You would be thrown through the windshield of the car due to inertia. 
Q19: A bowling ball in motion tends to remain in motion unless acted on by an outside force. Why is it difficult to start a bowling ball moving? 
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A19: The bowling ball has significant mass for its size. Its inertia due to its mass makes it resist movement. 
Q110: You are in an airplane cruising at 500 km/hr. You jump straight up in the aisle of the airplane. Where do you land and why? 
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A110: You and the airplane are traveling forward at the same speed. So, when you jump up, you come down in exactly the same spot. 
Q111: You are in an automobile cruising at 35 miles/hr. You toss a tennis ball up in the air. Where does it land and why? 
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A111: You, the automobile, and the tennis ball are traveling forward at 35 miles/hr. When you toss the ball up it is also going forward at 35 miles/hr. and will return to your hands. 
Q112: Explain how Newton's 1st Law is responsible for space travel. 
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A112: The rocket will stay on the launch pad until an outside force acts upon it. Also, rockets going to the moon only have to fire the rockets to get started. The rocket will coast the rest of the way to the moon. 
Q21: State and give an example of Newton's 2nd Law of Motion. 
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A21: The unbalanced force acting on an object equals the object's mass times its acceleration. Using F=ma, the greater the force on a soccer ball, the greater its acceleration. 
Q22: From the picture of the football players on page 400, explain why the two players in the picture on the right get less acceleration. 
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A22: They achieve less acceleration given the same force because the mass of the sled has increased. 
Q23: What is the formula for FORCE? 
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A23: F = m * a F = ma 
Q24: What is the unit of measurement for FORCE? 
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A24: Newtons (N) 
Q25: What are balanced forces? 
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A25: Balanced forces are equal and opposite in direction. Balanced forces do not change motion. In other words, they cancel each other. 
Q26: What are unbalanced forces? 
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A26: Unbalanced forces are not equal or opposite in direction. They do not cancel completely. 
Q27: Describe Newton's 2nd Law of Motion in terms of acceleration. 
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A27: The acceleration of an object is directly proportional to the net force on the object. The more acceleration, the more force. 
Q28: Why does a small sports car have better acceleration than an 18wheel truck? 
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A28: A small sports car has much less mass. Therefore, it takes less force for the sports car to accelerate than it does for the truck. 
Q29: Why does a small car have better fuel economy than a large SUV? 
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A29: A small car has much less mass than an SUV. The small car therefore takes less force (gas) to move. 
Q210: Explain how Newton's 2nd Law of Motion is responsible for space travel. 
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A210: Scientists had to calculate how much FORCE was needed in terms of thrust for the rocket engines to lift the MASS of the rocket into orbit. 
Q31: How are weight and mass related? 
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A31: Mass is how much matter is in a given object. Weight is determined by the planet you are on. So, you would weight 1/6 of your current weight on the moon because its gravitational pull is 1/6 that of earth. 
Q32: What is "weight?" 
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A32: Weight is the measure of the gravitational force exerted on an object. 
Q33: How do you calculate "weight" on the moon? 
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A33: Moon Weight = your weight on Earth * 1.6 m/s/s 
Q34: What is the unit of measurement for WEIGHT? 
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A34: Newtons (N) 
Q35: What is the difference between MASS and WEIGHT? 
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A35: Mass is how much matter an object has. Weight can vary depending on the planet's gravitational pull. 
Q36: Using the table on page 404 and the paragraph beside it, calculate the weight of a 66kg person on a) Earth, b) Venus, c) Mars, d) Neptune, and 3) the moon. 
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A36: Earth: 66kg * 9.8m/s/s = 646.8N 
Q37: What is the Law of Universal Gravitation? 
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A37: All objects in the universe attract each other through the force of gravity. 
Q38: Why can you feel the presence of gravity between you and the Earth, but not between you and a pencil? 
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A38: a) The earth is massive and so it has lots of gravity. When you jump up, you come down due to earth's gravity. b) Neither you nor your pencil have much gravity because you and the pencil have little mass. 
Q39: Gravity is dependent on two factors. What are they? 
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A39: Distance and Mass 
Q310: As the distance between two objects decreases, the force of gravity between them ......... . 
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A310: Increases 
Q311: What happens to the gravitational force between two objects if their masses do not change but the distance between them becomes 2 times as much? 
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A311: As distance doubles, the gravitational attraction drops to 1/4 as much. F = G*(m_{1}*m_{2})/d^{2} 
Q312: The weight of an object varies with the ......................... . 
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A312: gravitational acceleration of the planet. 
Q41: What is "free fall?" 
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A41: Free Fall is the motion of a body when only the force of gravity is acting on the body. 
Q42: What is "terminal velocity?" 
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A42: Terminal Velocity is the constant velocity of a falling object when the force of air resistance is equal in magnitude and opposite in direction to the force of gravity. 
Q43: In the picture of the sky diver on page 407 air resistance and gravity are balanced. Is the skydiver at rest? Why or why not? 
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A43: NO! If the forces are balanced it just means that the skydiver is no longer picking up speed. In other words, he has reached "terminal velocity." 
Q44: What would be the main difference between a parachute for a person and a parachute for an airplane? 
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A44: To slow down an airplane , you would need a HUGE parachute! 
Q45: Why are astronauts in the orbiting space shuttle not really "weightless?" 
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A45: One cannot be truly "weightless" anywhere in the universe. It would be more accurate to say that they were experiencing "microgravity." 
Q46: What is projectile motion? 
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A46: Projectile Motion is the curved path than an object follows when thrown, launched, or otherwise projected near the surface of Earth. 
Q47: In the red and yellow ball illustration on page 409, why do both balls reach the ground at the same time? 
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A47: Even though the yellow ball was ejected to the right, gravity acts upon it the same way it does on the red ball. They both fall to the ground at 9.8 m/s/s. 
Q48: Why doesn't a thrown ball orbit the earth? 
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A48: It doesn't have enough acceleration. The ball would need a speed of 7906 m/s to achieve earth orbit. 
Q49: Name the two components that make up orbital motion, and explain why objects STAY in orbit. 
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A49: Forward motion and Free Fall motion due to gravity. The object stays in orbit because its forward motion is just enough to counteract the pull of gravity. 
Q410: A friend in an ultralight plane flies over you at an altitude of 200 feet at a speed of 35 miles/hr. He releases a water balloon directly over you. Does the water balloon hit you? Why or why not? 
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A410: NO! If the water balloon is released directly over your head, it will still be going at 35 miles/hr forward and will trace a projectile arc as it falls to the ground some distance away from you. 
Q51: State and give an example of Newton's 3rd Law of Motion. 
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A51: For every action force, there is an equal and opposite reaction force. If you are in a boat and try to step off the boat onto a dock, you will push the boat away from the dock as you step forward. 
Q52: Give two examples of how forces always occur in pairs. 
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A52: a) The action force is a swimmer pushing the water backwards. The reaction force is the water pushing the swimmer forward. b) A rocket fires thrust downward and the reaction is the rocket takes off. 
Q53: Why don't the forces in a force pair cancel each other? 
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A53: Action / Reaction forces never cancel out because they act on different objects. 
Q54: Explain your bottle rocket's action using Newton's 3rd Law of Motion. 
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A54: Action: Water and air shoot out of the bottom of the rocket. Reaction: The rocket takes off. 
Q55: If a horse pulls a cart with a certain horizontal force, the cart exerts an equal and opposite force on the horse. If this is so, how can the cart accelerate? 
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A55: The action of the horse is not against the cart, but against the ground. 
Q56: In the early 1900's many people thought that rockets could not work in space because there was no ground for the rocket to push off from. Explain why rockets work just fine in space. 
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A56: You don't need "ground" for the rocket to "push off" from. All you need is for the rocket engines to throw out massive amounts of "thrust" and off it goes. 
Q57: Explain how Newton's 2nd law of motion is responsible for space travel. 
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A57: Scientists needed to know the mass of the rocket and the acceleration needed for escape velocity in order to calculate how much force is needed at liftoff. 
Q61: Define momentum. 
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A61: Momentum is a quantity defined as the product of the mass and velocity of an object. P = m* v 
Q62: What is the formula for momentum? 
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A62: P = m* v 
Q63: To what two quantities is momentum proportional? 
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A63: mass and velocity 
Q64: When you apply a force to an object, do you change its momentum? 
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A64: YES! 
Q65: Why do cars have "crumple zones?" 
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A65: In order to slow down the rate of the collision. 
Q66: State the Law of Conservation of Momentum and give an example. 
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A66: The total amount of momentum in an isolated system is conserved. 
Q67: The mass of a ball is 2 kg. The ball is moving at 5 m/s. What is the momentum of the ball? 
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A67: m=2kg v=5m/s P=? 
Q71: State Newton's 1st Law of Motion and give an example. 
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A71: An object at rest remains at rest and an object in motion maintains its velocity unless it experiences a net force. A ball rolling across a table will continue until an outside force acts upon it. 
Q72: State Newton's 2nd Law of Motion and give an example. 
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A72: The unbalanced force acting on an object equals the object's mass times its acceleration. Using F=ma, the greater the force on a soccer ball, the greater its acceleration. 
Q73: What is the formula for FORCE? 
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A73: F= m * a 
Q74: Compare weight and mass. 
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A74: Mass is how much matter is in a given object. Weight is determined by the planet you are on. So, you would weigh 1/6 of your current weight on the moon because its gravitational pull is 1/6 that of earth. 
Q75: What is the Law of Universal Gravitation? 
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A75: All objects in the universe attract each other through the force of gravity. 
Q76: Define free fall. 
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A76: Free Fall is the motion of a body when only the force of gravity is acting on the body. 
Q77: Define projectile motion. 
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A77: Projectile Motion is the curved path than an object follows when thrown, launched, or otherwise projected near the surface of Earth. 
Q78: For Newton's 3rd Law of Motion, why don't actionreaction forces cancel out? 
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A78: Action / Reaction forces never cancel out because they act on different objects. 
Q79: What is the formula to determine momentum? 
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A79: P = m * v 
Q710: What happens to momentum in collisions? 
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A710: The total momentum of two or more objects after they collide is the same as it was before the collision. 
Q711: A wrestler weighs in for the first match on the moon. Will the athlete weigh more or less on the moon than he does on Earth? Use WEIGHT, MASS, FORCE, and GRAVITY in your answer. 
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A711: To determine the athlete's correct WEIGHT, multiply his MASS times the acceleration due to GRAVITY on the moon (1.6m/s/s) and you will have his FORCE or WEIGHT. 
Q712: You and a buddy are arm wrestling but seem to be matched in strength so that no movement occurs. Your hands are locked in the 12 o'oclock (upright) position. Describe the situation in terms of one of Newton's Laws of Motion. 
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A712: This illustrates balanced forces. You could use Newton's 1st law and say that no additional outside force is acting on the hands and so they remain motionless. You could use Newton's 2nd law and say that the forces applied are equal. 