Read the first worked example with the solution open so the structure is clear.
Try the practice problems before revealing each solution.
Use the related concepts and background knowledge badges if you feel stuck.
What to Focus On
Core idea:Position starts by naming what changes, over what time interval, and whether direction matters.
Common stuck point:Students often know a formula related to position but skip the recognition step: Am I describing motion over time with position, distance, direction, speed, velocity, or acceleration clearly separated? That leads to a correct-looking substitution attached to the wrong physical model.
Sense of Study hint:Ask: Am I describing motion over time with position, distance, direction, speed, velocity, or acceleration clearly separated?
Worked Examples
Example 1
easy
An object starts at position x=3 m and moves to x=11 m along a straight line. What is the object's displacement?
Answer
Δx=8 m
First step
1
Position is a specific location on a coordinate axis. The initial position is xi=3 m and the final position is xf=11 m.
Full solution
2
Displacement is the change in position: Δx=xf−xi=11−3=8 m
3
The displacement is 8 m in the positive direction.
Position describes where an object is located relative to a chosen origin. Displacement is the change in position and is independent of the path taken between the two positions.
Example 2
medium
A particle's position is given by x(t)=4t2−2t+1 (in meters, with t in seconds). What is the particle's position at t=0 s and t=3 s? What is the displacement between these times?
Example 3
medium
A bug's position is x(t)=2t+1 (meters, t in seconds). What is its position at t=4 s?
Example 4
medium
A car's position is x(t)=5t2 meters. Find its position at t=2 s and t=5 s, then the displacement between these times.
Example 5
medium
A ball's position is y(t)=20−5t2 meters (up positive, ground at y=0). At what time does it hit the ground?
Example 6
hard
A particle's position is x(t)=t2−6t+5 (meters). At what times is the particle at x=0?
Example 7
hard
A ball's position is y(t)=1.5+10t−5t2 meters (up positive). Find the time of maximum height and the maximum height above the ground.
Example 8
challenge
A train sits at position xT=+120 m in the platform frame. The platform frame moves at +5 m/s relative to a car frame; at t=0 the two frames' origins coincide. What is the train's position in the car frame at t=4 s (treat the train as instantaneously at rest in the platform frame)?
Practice Problems
Try these problems on your own first, then open the solution to compare your method.
Example 1
medium
An ant walks from position x=−5 m to x=7 m, then back to x=2 m. What is the total distance traveled and the final displacement from the starting point?
Example 2
hard
A particle's position is x(t)=t3−6t2+9t (meters). At what times is the particle at position x=0? What is the velocity at each of those times?
Example 3
easy
A point is at x=5 m on a number line whose origin is the front door. What is its position?
Example 4
easy
An ant sits 3 m left of the origin. Taking right as positive, what is its position?
Example 5
easy
A car is at the 20 km marker on a highway measured from town. State its position relative to town.
Example 6
easy
Object A is at x=2 m and object B is at x=9 m. Which has the larger coordinate?
Example 7
easy
A runner starts at the origin. Where is the origin's position coordinate?
Example 8
easy
Taking up as positive, a drone hovers 12 m above the ground origin. Its position?
Example 9
easy
A bead is at x=−4 cm. Is it left or right of the origin if right is positive?
Example 10
easy
Two flags are placed at x=10 m and x=10 m in the same frame. Are they at the same position?
Example 11
medium
A cyclist's position is x=3 m at the start and x=11 m later, same frame. By inspection, on which side of the start is she now and how far along the axis?
Example 12
medium
A train's position relative to the platform is xp=+50 m, but relative to a moving car the same train is at xc=−20 m. Why do they differ?
Example 13
medium
On an x-axis (right positive), point P is 7 m right of origin and point Q is 5 m left. Give both positions and which is greater.
Example 14
medium
A snail is at x=2 m. The origin is shifted 2 m to the right (new origin where the snail was). What is the snail's new position coordinate?
Example 15
medium
A hiker's positions at three times are x=0,4,1 m. Which is the maximum position and which the minimum?
Example 16
medium
A ball on a vertical axis (up positive) is at y=+6 m then later at y=−2 m. Has it ended above or below the origin?
Example 17
challenge
A car's position is x=120 m from town A and x=80 m from town B (towns are on a line, A left of B). If A is the origin, what is B's position coordinate?
Example 18
challenge
Positions of a particle (in m) follow x(t)=t2−4t for t in seconds. At what time is the particle back at the origin (other than t=0)?
Example 19
challenge
A point moves so its position is x=−3 m, then origin is redefined at x=−3 m AND positive direction is reversed. What is the point's new coordinate?
Example 20
medium
Three checkpoints are at x=2,7,15 m. A scout claims the middle checkpoint is exactly halfway between the outer two. Is the claim true?
Example 21
medium
On a number line (right positive), a car moves so its position goes −6 m, 0 m, +4 m at three times. State which reading is farthest from the origin.
Example 22
medium
A marker is at x=15 m from gate A. Gate B is 9 m right of gate A. What is the marker's position measured from gate B?
Example 23
easy
A book sits on a shelf 1.4 m above the floor. Taking the floor as the origin and up as positive, what is the book's position?
Example 24
easy
Two pens lie on a desk. Pen A is at x=12 cm and pen B is at x=5 cm from the desk's left edge. Which pen is farther from the origin?
Example 25
easy
A swimmer is at x=−8 m and a buoy is at x=−3 m on the same axis (right positive). Which has the LARGER coordinate?
Example 26
easy
A rock sits on the bottom of a pond, 2.5 m below the water surface. Taking the surface as origin and up as positive, what is the rock's position?
Example 27
medium
A particle moves with x(t)=10−3t (meters). At what time does it cross the origin?
Example 28
medium
On a 2D map taking east-x and north-y positive, a hiker is 300 m east and 400 m north of camp. Give her position as a coordinate pair, and her straight-line distance from camp.
Example 29
medium
A mouse is at x=0.40 m relative to the corner of a desk. If the origin is moved 0.15 m to the right, what is the mouse's new position coordinate?
Example 30
medium
A delivery truck is at mile marker 42 on a highway. Its depot is at mile marker 30. Taking the depot as origin and increasing markers as positive, what is the truck's position?
Example 31
medium
A skateboarder's positions at t=0,1,2,3 s are 0,3,8,15 m. Is the motion uniform (constant velocity)?
Example 32
medium
Town A is the origin. Town B is 40 km east of A. A truck is 25 km east of B. Find the truck's position in A's frame.
Example 33
medium
A scientist tracks the position of a particle at three times: x1=+4, x2=−2, x3=+1 meters. What is the largest absolute displacement between any pair of these readings?
Example 34
medium
A ladybug starts at x=8 cm and walks until it reaches x=−2 cm. Find the displacement.
Example 35
hard
Two cars share an x-axis. Car A's position is xA(t)=5t, car B's is xB(t)=30−5t (meters). At what time and position do they meet?
Example 36
hard
A particle has x(t)=3t2−12t+7 meters. Find the time and value of its minimum position.
Example 37
challenge
A particle's position is x(t)=t3−9t meters. At what times is the particle exactly 4 m from the origin?