Physics Ch. 3 – Flashcards
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As you read this in your chair, how fast are you moving relative to the chair? Relative to the Sun?
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You are not moving relative to the chair, but you are moving over 100,000 km/h relative to the Sun.
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What two units of measurement are necessary for describing speed?
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Distance and time
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What kind of speed is registered by an automobile speedometer?
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Instantaneous speed
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What is the average speed in kilometers per hour of a horse that gallops a distance of 15 km in a time of 30 min?
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30 km/hr
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How far does a horse travel if it gallops at an average speed of 25 km/h for 30 min?
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12.5 km
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What is the main difference between speed and velocity?
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Velocity includes a direction, but speed does not.
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If a car moves with a constant velocity, does it also move with a constant speed?
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Yes, because constant velocity requires constant speed in the same direction.
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If a car is moving at 90 km/h and it rounds a corner, also at 90 km/h, does it maintain a constant speed? A constant velocity?
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It maintains a constant speed, but does not maintain a constant velocity.
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What is the acceleration of a car moving along a straight road that increases its speed from 0 to 100 km/h in 10 s?
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10 km/h·s
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What is the acceleration of a car that maintains a constant velocity of 100 km/h for 10 s?
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0 km/h·s
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When are you most aware of your motion in a moving vehicle: when it is moving steadily in a straight line or when it is accelerating? If you were in a car that moved with absolutely constant velocity (no bumps at all), would you be aware of the motion?
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Accelerating. You would not be aware of the motion if you did not look outside the car.
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Acceleration is generally defined as the time rate of change of velocity. When can it be defined as the time rate of change of speed?
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When moving in a straight line, the time rate of change of speed is acceleration.
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What did Galileo discover about the amount of speed a ball gained each second when rolling down an inclined plane? What did this say about the ball's acceleration?
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The ball had constant acceleration, so it gained the same speed every second.
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What relationship did Galileo discover about a ball's acceleration and the steepness of an incline? What acceleration occurs when the plane is vertical?
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The steeper the incline, the greater the acceleration. On a vertical incline, the ball is in free fall.
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What exactly is meant by a "freely falling" object?
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An object in free fall falls under gravity alone with no friction.
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What is the gain in speed per second for a freely falling object?
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It gains approximately 10 m/s.
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What is the speed acquired by a freely falling object 5 s after being dropped from a rest position? What is the speed 6 s after?
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The speed is 50 m/s after 5 s and 60 m/s after 6 s.
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The acceleration of free fall is about 10 m/s2. Why does the seconds unit appear twice?
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The second appears once in the denominator of the unit for speed and once for the interval of time.
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When an object is thrown upward, how much speed does it lose each second (ignoring air resistance)?
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It loses 10 m/s of speed each second until it reaches the high point, then it gains 10 m/s each second.
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What relationship between distance traveled and time did Galileo discover for freely falling objects released from rest?
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Galileo discovered that distance increased as the time squared.
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What is the distance fallen for a freely falling object 1 s after being dropped from a rest position? What is the distance for a 4-s drop?
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It falls 5 m in 1 s and 80 m in 4 s.
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What is the effect of air resistance on the acceleration of falling objects?
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Air resistance decreases the acceleration of falling objects.
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Given the measurements 10 m, 10 m/s, and 10 m/s2, which is a measure of speed, which is a measure of distance, and which is a measure of acceleration?
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10 m is distance, 10 m/s is speed, and 10 m/s2 is acceleration.
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What is the speed over the ground of an airplane flying at 100 km/h relative to the air caught in a 100-km/h right-angle crosswind?
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141 km/h
