NEB Class 11 • Physics • Mechanics

Kinematics: NEB Class 11 Physics Guide

Describe motion precisely with position, displacement, velocity, acceleration, graphs and constant-acceleration models before connecting it to forces.

Concept distinctions that prevent formula misuse
Graph slopes and areas explained physically
Worked Nepal-context examples, practice and FAQs

Curriculum and source boundary

Where Kinematics fits in NEB Class 11 Physics

Kinematics follows physical quantities and vectors because motion is described through measurable, often directional quantities. It supplies the language used later in dynamics: position, displacement, velocity and acceleration. The current CDC Physics Grade 11 page is the Nepal scope checkpoint. The OpenStax kinematics introduction makes the central boundary clear: kinematics describes motion, while dynamics studies its causes.

Review the Class 11 Vectors guide if signed directions or components are weak. A one-dimensional motion problem is still vector reasoning expressed along one chosen axis. A negative velocity does not mean “slow”; it means motion opposite the positive direction.

Build the motion story

Position, distance, displacement, speed and velocity

Position x locates an object relative to an origin along a coordinate axis. Displacement Δx = x_f − x_i records the change in position. Distance is the total path length and is scalar. A person walking 50 m east and 20 m west covers 70 m but has a displacement of 30 m east.

Average speed is total distance divided by elapsed time. Average velocity is displacement divided by elapsed time. Instantaneous velocity describes the rate and direction of position change at one moment. An odometer-like path total and a velocity vector answer different questions, so the words cannot be interchanged.

Quantity	Core meaning	Graph connection	Common trap
Position x	Location relative to origin	Vertical value on x–t graph	Treating origin as physically special
Displacement Δx	Final minus initial position	Change in x	Adding all path lengths
Velocity v	Rate of change of position	Slope of x–t graph	Calling negative velocity “deceleration”
Acceleration a	Rate of change of velocity	Slope of v–t graph	Assuming acceleration follows motion

Average acceleration is Δv/Δt. Acceleration may be opposite velocity when an object slows, in the same direction when its speed grows, or perpendicular in curved motion when direction changes. “Negative acceleration” only identifies direction relative to the chosen axis; it does not automatically mean slowing down.

Graphs compress a motion story

How to read position–time, velocity–time and acceleration–time graphs

On a position–time graph, slope represents velocity. A straight rising line has constant positive velocity; a horizontal line means constant position; a curve with increasing slope shows changing velocity. The area under a position–time graph has no standard kinematic meaning, so do not apply the “area rule” to every graph.

On a velocity–time graph, slope is acceleration and signed area is displacement. Area below the time axis contributes negative displacement. Total distance requires adding absolute area magnitudes for each interval. On an acceleration–time graph, signed area gives change in velocity, not final velocity unless the initial velocity is then included.

x–t graph

Ask: where is the object and how steep is the curve? Tangent slope gives instantaneous velocity.

v–t graph

Ask: which direction, how fast and how is velocity changing? Slope gives acceleration; area gives displacement.

a–t graph

Ask: how quickly and in which direction is velocity changing? Area gives Δv.

A graph crossing zero does not always mean the same event. Position crossing zero means passing the chosen origin. Velocity crossing zero means momentarily stopping and possibly reversing. Acceleration crossing zero means velocity is momentarily not changing, not necessarily that the object is at rest.

Model with conditions

Equations of motion for constant acceleration

When acceleration is constant, velocity changes uniformly and a useful set of equations follows from the definitions. The OpenStax constant-acceleration treatment emphasizes identifying knowns, the unknown and the valid model before selecting an equation.

v = u + at | s = ut + ½at² | v² = u² + 2as | s = ½(u + v)t

Here u is initial velocity, v final velocity, a constant acceleration, t elapsed time and s displacement during the interval. These equations are not universal motion formulas. If acceleration changes substantially, divide motion into intervals or use graphical/calculus methods appropriate to the course.

Sketch and choose positive direction. Write the direction beside the axis.
List knowns with signs. “From rest” means u = 0; it does not mean position is zero.
State the model. Confirm that acceleration is constant over the interval.
Select by variables. Choose an equation containing the unknown and available knowns.
Solve symbolically first. This exposes sign and unit relationships.
Interpret. A negative time usually signals a setup error; a negative velocity indicates direction.

One important constant-acceleration model

Free fall and vertical motion

Near Earth’s surface and when air resistance is neglected, freely falling objects share a downward acceleration g. Choose upward as positive and acceleration becomes a = −g; choose downward as positive and a = +g. Either convention works if used consistently.

At the highest point of a vertical throw, instantaneous velocity is zero but acceleration remains downward. The object has not “lost gravity.” This distinction is a frequent conceptual question. The OpenStax free-fall reference connects vertical motion to the same constant-acceleration framework.

Model warning: Use the current course value and convention for g. Air resistance, altitude and measurement precision determine how closely the ideal model matches a real fall.

Two directions, one clock

Projectile motion as independent components

A projectile model separates horizontal and vertical motion. With negligible air resistance, horizontal acceleration is zero and horizontal velocity is constant, while vertical acceleration is downward. Both components share the same time. The OpenStax two-dimensional motion section uses vector components to describe displacement and velocity.

Resolve launch velocity u into u_x = u cos θ and u_y = u sin θ when θ is measured above horizontal. Apply one-dimensional equations separately. Do not insert total speed into a vertical equation or use different times for the two components.

For launch and landing at the same height in the ideal model, the vertical velocity component reverses sign while the horizontal component is unchanged. Speed magnitudes at equal heights match, but velocity vectors do not because their vertical directions differ.

Worked examples

From words and graphs to motion quantities

Example 1: average speed and velocity

A student walks 120 m east in 80 s, then 40 m west in 20 s. Distance = 160 m, displacement = 80 m east and total time = 100 s. Average speed = 1.60 m s⁻¹; average velocity = 0.80 m s⁻¹ east.

Check: Average-speed magnitude is larger because path length exceeds displacement magnitude.

Example 2: bus acceleration

A bus starts from rest and accelerates uniformly at 1.5 m s⁻² for 8.0 s. Final velocity v = 0 + 1.5 × 8.0 = 12 m s⁻¹. Displacement s = ½ × 1.5 × 8.0² = 48 m.

Check: Average velocity for constant acceleration is (0 + 12)/2 = 6 m s⁻¹; 6 × 8 = 48 m.

Example 3: braking sign

A motorcycle moving at 20 m s⁻¹ east stops uniformly in 5.0 s. Take east positive. a = (0 − 20)/5.0 = −4.0 m s⁻². Displacement s = ½(20 + 0) × 5.0 = 50 m east.

Meaning: Negative acceleration here is westward and opposite positive velocity, so speed decreases.

Example 4: velocity–time area

Velocity rises linearly from 2 to 10 m s⁻¹ over 4 s. Acceleration is the slope: (10−2)/4 = 2 m s⁻². Displacement is trapezium area: ½(2+10)×4 = 24 m.

Check: Average velocity 6 m s⁻¹ for 4 s also gives 24 m.

Reliable problem solving

A six-step method for Kinematics questions

Translate the story into an axis, origin, time interval and simple sketch.
Separate distance from displacement and speed from velocity.
List variables with signs and SI units; convert kilometres per hour when necessary.
Decide whether the graph, a definition or a constant-acceleration model applies.
Solve without premature rounding, then state direction and unit.
Check dimensions, graph shape, sign, limiting case and physical plausibility.

The companion Kinematics study guide gives a diagnostic and revision plan. Use the Kinematics practice set when you can explain the ideas and need mixed problem evidence.

Common traps

Mistakes that change the physical story

Distance equals displacement

They match only when motion does not reverse along a straight path. Track endpoint change separately from path length.

Negative means slowing

Signs show direction. Speed decreases only when acceleration and velocity have opposite directions.

Using SUVAT everywhere

Constant-acceleration equations require constant acceleration. A curved v–t graph usually signals a changing value.

Confusing slope and area

Write the axes and units. Slope divides vertical change by horizontal change; area multiplies them.

Try without notes

Practice and self-check

Sketch an x–t graph for rest, constant positive velocity and increasing positive velocity.
A cyclist changes from 4 to 10 m s⁻¹ in 3 s. Find average acceleration.
A stone is released from rest. State velocity and acceleration directions during the fall.
A v–t graph is 6 m s⁻¹ for 5 s and then −2 m s⁻¹ for 3 s. Find displacement and distance.
Explain why velocity can be zero while acceleration is non-zero.
Design a constant-acceleration problem solvable without time and identify the appropriate equation.

Readiness: You should be able to draw a motion diagram, select a model from conditions, derive graph quantities with units and explain the sign of every vector. For online or physical tuition, call 9846662070.

Frequently asked questions

Questions students ask about Kinematics

What is Kinematics in Class 11 Physics?

Kinematics describes motion through position, displacement, velocity and acceleration without first analysing the forces that cause the motion.

What is the difference between distance and displacement?

Distance is total path length and is scalar. Displacement is final position minus initial position and includes direction.

Does negative acceleration always mean slowing down?

No. Speed decreases when acceleration is opposite velocity. If both velocity and acceleration are negative, speed can increase in the negative direction.

When can I use equations of motion?

Use the common equations when acceleration is constant over the interval and your signs and variables refer to one consistent axis.

What does area under a velocity–time graph represent?

Signed area under a velocity–time graph gives displacement. Add absolute interval areas to obtain total distance.

Where can I get help with NEB Class 11 Kinematics?

For current online or physical tuition options, call 9846662070 and confirm schedule, class mode, teacher availability and fees.

References and next steps

Sources and related study guides

Continue with Dynamics to connect acceleration with net force, after completing the Kinematics practice set. Sources and scope were checked on 2 August 2026; follow current CDC, NEB and college instructions if assessment requirements change.

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