9702 · 3.2
Non-uniform motion flashcards
Revision flashcards for Cambridge 9702 Non-uniform motion (syllabus 3.2). Flip, recall, then mark a real past-paper question.
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What is the primary characteristic that defines non-uniform motion?
A changing velocity (i.e., acceleration or deceleration) of an object.
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How does Newton's Second Law quantitatively relate resultant force, mass, and acceleration?
It states that resultant force equals mass times acceleration ($F = ma$). The acceleration's direction matches the resultant force.
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How can force be alternatively defined in terms of momentum?
Force is the rate of change of an object's momentum over time ($F = \frac{\Delta p}{\Delta t}$).
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Explain the conditions under which an object falling through a fluid reaches terminal velocity.
Terminal velocity is reached when the downward driving force (weight) is balanced by the total upward resistive forces (air resistance, upthrust), resulting in zero net force and constant velocity.
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How does air resistance typically impact the trajectory of a projectile?
Air resistance reduces both the maximum height attained and the horizontal range covered by the projectile, and makes the trajectory asymmetrical.
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State Newton's First Law of Motion.
An object will remain at rest or continue at a constant velocity unless acted upon by a resultant force.
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What is momentum and how is it calculated?
Momentum ($p$) is a vector quantity defined as an object's mass ($m$) multiplied by its velocity ($v$), so $p = mv$.
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What is the key difference between Newton's Second Law and Third Law?
Newton's Second Law relates force, mass, and acceleration for a single object, while Newton's Third Law describes action-reaction force pairs acting on *different* objects.
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Define weight and state its formula.
Weight ($W$) is the gravitational force on an object, calculated as its mass ($m$) multiplied by the acceleration due to gravity ($g$), so $W = mg$.
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What factors increase air resistance on a falling object?
Increased speed, larger cross-sectional area, and specific shape of the object, as well as the fluid's density/viscosity.
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Why is $F = \frac{\Delta p}{\Delta t}$ considered a more general form of Newton's Second Law than $F = ma$?
Because it applies to systems where mass is not constant (e.g., a rocket expelling fuel), whereas $F = ma$ is only valid for objects with constant mass.
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Why don't the action-reaction force pairs in Newton's Third Law cancel each other out?
Because they act on two different objects. To find the net force on an object, you only sum the forces acting *on that single object*.
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Describe the shape of a velocity-time graph for an object falling from rest and reaching terminal velocity.
The graph starts at the origin with a steep positive gradient. The gradient gradually decreases (curve becomes less steep) as velocity increases, eventually becoming zero (a horizontal line) when terminal velocity is reached.
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How does air resistance affect the trajectory of a projectile compared to an ideal parabolic path?
Air resistance makes the trajectory asymmetrical. It reduces the maximum height and horizontal range, and makes the angle of descent steeper than the angle of ascent.