Physics Chapter 2 Problems and Concepts – Flashcards
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What class of motion, natural or violent, did Aristotle attribute to motion of the moon?
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Natural motion
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What relationship between the Sun and Earth did Copernicus formulate?
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Heliocentric
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What type of path does a moving object follow in the absence of a force?
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Straight-line
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What is the net force on a cart that is pulled to the right with 100 pounds of force and to the left with 30 pounds of force?
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70 pounds to the right
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If Nellie was hanging on two ropes vertically without an angle involved, what would be the tension in each rope?
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Half of her weight
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What does it mean to say something is in mechanical equilibrium?
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All forces acting on an object are vectorally zero
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Consider a book that weighs 15 N at rest on a flat table. How many Newtons of support force does the table provide? What is the net force on the book?
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Support force is 15 N; net force is 0 N
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A bowling ball at rest is in equilibrium. Is the ball in equilibrium when it moves at constant speed in a straight-line path? What type of equilibrium?
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Yes; Dynamic equilibrium
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What concept was not understood in the 16th century when people couldn't conceive of a moving Earth?
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Inertia
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A bird sitting in a tree is traveling at 30 km/s relative to the faraway Sun. When the bird drops to the ground below, does it still move at 30 km/s, or does this speed become zero?
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The bird still moves at 30 km/s relative to the Sun
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Lucy Lightfoot stands with one foot on one bathroom scale and her other foot on another. Each scale reads 350 N. What is Lucy's weight?
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700 N
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What Aristotlean idea did Galileo discredit in his fabled Leaning Tower demonstration?
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Falling-body hypothesis which states that bodies fall faster if they are heavier
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A space probe may be carried by a rocket into outer space. What keeps the probe moving after the rocket no longer pushes it?
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Nothing keeps it moving. The absence of a propelling or deflecting force simply keeps it moving in a straight line.
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When any object is in mechanical equilibrium, what can be correctly stated about all the forces that act on it? Must the net force necessarily be zero?
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The net force is zero, and it must be zero
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A hockey puck slides across the ice at a constant speed. Is it in equilibrium? Why or why not?
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Yes, because it reaches dynamic equilibrium when it moves in a straight line with unchanging speed. The net forces are zero.
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If a strong man exerts a downward force of 800 N on a pulley system, how much upward force is exerted on the rope?
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800 N upwards; the pulley simply redirects force
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Two people each pull with a force of 300 N on a rope. What is the net force on the rope? How much force is exerted by each person on the rope?
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Net force is zero; each person exerts 300 N of force in opposite directions
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When you push on a cart, it moves. When you stop pushing, it comes to rest. Does this violate Newton's law of inertia?
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No, it is the result of friction acting between the cart and the floor. An external force acts on the system.
