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Flashcards · 9702 · AS Topic 2
Kinematics (AS Level) flashcards
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2.1 Equations of motion
- The four equations of motion, and the condition for using them
- v = u + at s = ut + ½at² v² = u² + 2as s = (u + v)t ÷ 2 Valid only for uniform (constant) acceleration.
- Derive v = u + at
- Acceleration is the rate of change of velocity: a = (v − u) ÷ t. Rearranging: at = v − u, so v = u + at.
- Velocity–time graph: what do the gradient and the area give?
- Gradient: acceleration. Area under the line: displacement (area below the time axis counts as negative displacement).
- How do you find the velocity at an instant from a curved displacement–time graph?
- Draw the tangent to the curve at that instant and find its gradient (not the gradient of a chord between two points).
- The key method for projectile motion
- Treat horizontal and vertical motion independently; they share only the time. Horizontal: a = 0, constant velocity. Vertical: a = g downwards, use the equations of motion.
- A ball is thrown at 20 m s⁻¹ at 30° above the horizontal. Find its initial velocity components.
- Horizontal: 20 cos 30° = 17.3 m s⁻¹. Vertical: 20 sin 30° = 10 m s⁻¹.
- At the top of a projectile’s path, which velocity component is zero?
- The vertical component. The horizontal component is unchanged (with no air resistance).
- How can g be determined by a free-fall experiment?
- Drop an object from rest through a measured height s, timing the fall electronically (light gates or an electromagnet release). s = ½gt², so g = 2s ÷ t². Repeat and average t.