Maths347 views·Updated May 17, 2026·4 pages

Understanding Kinematics: Mechanics and Constant Acceleration

Jessie M@studywithjessie

Kinematics is all about tracking how objects move through space... Show more

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$Kinematics Revision V= $\frac{d}{dt}$r differentiate Displacement (r) Notation:$

Kinematics Fundamentals

Think of kinematics like a GPS system for physics - it tracks position, velocity, and acceleration of moving objects. These three concepts are connected through differentiation and integration, making calculus your best mate for solving motion problems.

Displacement (r) tells you where a particle is located relative to a starting point. You can find this using coordinates (x, y) and calculate the distance with |r| = √ $x² + y²$ . The displacement vector r is always underlined to show it's a vector quantity.

Velocity (v) shows how quickly position changes over time. You get this by differentiating displacement: v = dr/dt = (ẋ, ẏ). The speed is just the magnitude: |v| = √(ẋ² + ẏ²). Remember, velocity has direction whilst speed doesn't.

Acceleration (a) measures how velocity changes over time. It's the second derivative of displacement: a = dv/dt = d²r/dt² = (ẍ, ÿ). This tells you if something's speeding up, slowing down, or changing direction.

Quick Tip: Use dot notation (ẋ, ẏ) for first derivatives and double dots (ẍ, ÿ) for second derivatives - it's much faster than writing d/dt every time!

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$Kinematics Revision V= $\frac{d}{dt}$r differentiate Displacement (r) Notation:$

Finding When Particles Meet

When two particles are moving through space, you can predict exactly when and where they'll cross paths by setting their position vectors equal to each other. It's like solving a collision problem in a video game!

For the example with particles E and F, you need to match up the i and j components separately. Set the i coefficients equal: -11 + 5t = 13 + t, which gives you t = 6s. Then do the same for j components: 23 - 3t = -7 + 2t, which also gives t = 6s.

Since both calculations give the same time, the particles definitely meet at t = 6 seconds. If you'd got different times, it would mean the particles never actually cross paths - they'd just pass by each other at different heights or distances.

To find the meeting position, substitute t = 6 back into either position vector. You should get the same answer from both particles: $19i + 5j$ m. This confirms your calculation is spot on!

Pro Tip: Always check your answer by substituting the time into both position vectors - if they don't match, you've made an error somewhere!

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$Kinematics Revision V= $\frac{d}{dt}$r differentiate Displacement (r) Notation:$

Distance Between Moving Particles

Finding when particles are closest together or a specific distance apart involves working with relative displacement - basically tracking one particle from the perspective of the other. This technique is brilliant for collision avoidance problems!

Start by finding the relative displacement: rₐ - rᵦ. This gives you a single vector equation that describes how far apart the particles are. In the example, this becomes $6-t$ i + $4-t$ j, which represents the separation between particles A and B.

The distance squared is d² = $6-t$ ² + $4-t$ ² = 2t² - 20t + 52. For part (a), set d² = 100 $since distance = 10m$ and solve the quadratic to get t = 2s and t = 12s. The particles are 10m apart at both these times!

For part (b), find when particles are closest by differentiating d² and setting it to zero: d(d²)/dt = 4t - 20 = 0, giving t = 5s. At this moment, the particles are as close as they'll ever get during their motion.

Remember: When finding minimum distance, you're looking for when the rate of change of distance squared equals zero - that's your closest approach!

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$Kinematics Revision V= $\frac{d}{dt}$r differentiate Displacement (r) Notation:$

2D Motion Visualization

Understanding motion in 2D means tracking both x and y coordinates as they change over time. Think of it like plotting a character's movement across a game map - you need both horizontal and vertical positions to know exactly where they are.

The position vector r = (x(t), y(t)) gives you coordinates at any time t. In the example, r = $t², t-1$ traces out a curved path as t goes from 0 to 4. You can literally plot this on a graph to see the particle's journey!

Velocity vectors act like tangent lines to the path, showing the direction of movement at each instant. When t = 3, v = (6, -1), and when t = 4, v = (8, -1). Notice how these vectors point along the curve's direction at those specific moments.

The acceleration vector a = (2, 0) stays constant throughout this motion, always pointing horizontally to the right. This constant rightward acceleration gradually curves the particle's path, even though it starts moving diagonally.

Visual Learning: Try sketching the path and drawing velocity vectors at different points - you'll see how they're always tangent to the curve!

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Maths347 views·Updated May 17, 2026·4 pages

Understanding Kinematics: Mechanics and Constant Acceleration

Jessie M@studywithjessie

Kinematics is all about tracking how objects move through space and time - something you experience every day when you're walking, driving, or even just watching a ball fly through the air. This topic connects displacement, velocity, and acceleration using... Show more

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$Kinematics Revision V= $\frac{d}{dt}$r differentiate Displacement (r) Notation:$

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Kinematics Fundamentals

Quick Tip: Use dot notation (ẋ, ẏ) for first derivatives and double dots (ẍ, ÿ) for second derivatives - it's much faster than writing d/dt every time!

of 4

$Kinematics Revision V= $\frac{d}{dt}$r differentiate Displacement (r) Notation:$

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Finding When Particles Meet

To find the meeting position, substitute t = 6 back into either position vector. You should get the same answer from both particles: $19i + 5j$ m. This confirms your calculation is spot on!

Pro Tip: Always check your answer by substituting the time into both position vectors - if they don't match, you've made an error somewhere!

of 4

$Kinematics Revision V= $\frac{d}{dt}$r differentiate Displacement (r) Notation:$

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Distance Between Moving Particles

Remember: When finding minimum distance, you're looking for when the rate of change of distance squared equals zero - that's your closest approach!

of 4

$Kinematics Revision V= $\frac{d}{dt}$r differentiate Displacement (r) Notation:$

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2D Motion Visualization

Visual Learning: Try sketching the path and drawing velocity vectors at different points - you'll see how they're always tangent to the curve!