Kinematics word problems: the solving recipe
The universal recipe: draw, define the frame, list the five quantities, pick the equation, check signs.
In this lesson
- The universal recipe: draw, define the frame, list the five quantities, pick the equation, check signs.
Every kinematics problem dies by the same five-step ritual.
1) Sketch and mark the origin and +x direction. 2) List u, v, a, s, t with values and question marks. 3) Choose the equation with exactly the knowns + the unknown. 4) Solve with units. 5) Sanity-check magnitude and sign.
Word problems hide the data in sentences — translate 'comes to rest' as v = 0, 'dropped' as u = 0, 'retardation' as negative a.
The workhorse equations
Worked example
A body moves with v = 10 m/s for 3 s, then v = 5 m/s for 2 s in the same direction. Find the total distance.
- Distance = area under the v–t graph.
- 10×3 + 5×2 = 30 + 10 = 40 m.
Answer: 40
Transcript (0 min)
WEBVTT 1 00:00:00.000 --> 00:00:05.000 Kinematics word problems: the solving recipe — FemtoLearn. 2 00:00:05.000 --> 00:00:15.000 The universal recipe: draw, define the frame, list the five quantities, pick the equation, check signs.
Frequently asked
What is the most common mistake?
Applying constant-acceleration equations when a varies, or misassigning signs.
Practice
Free · 4 questions with full solutions- Q1 · Numerical · difficulty 2/5
A body moves with v = 10 m/s for 3 s, then v = 5 m/s for 2 s in the same direction. Find the total distance.
- Q2 · Numerical · difficulty 2/5
A body starts from rest with a = 4 m/s². Find the displacement in the 5th second.
- Q3 · Numerical · difficulty 2/5
A body starts from rest and accelerates uniformly at 9.5 m/s². Find the displacement in the 8th second of its motion.
- Q4 · Numerical · difficulty 2/5
The acceleration of a body starting from rest is a = 2 m/s² for 4 s, then zero for 2 s. Find its velocity at t = 6 s.