Describing Motion — Drills · Grade 12 Science
Chapter: Motion & KinematicsWhat these drills covers
By the end of Describing Motion you should be able to:
- I can describe an object's position relative to a chosen origin and reference frame.
- I can distinguish distance from displacement, and scalars from vectors, and calculate a resultant displacement.
- I can explain how the same motion looks different from different frames of reference.
6 questions, numeric, multiple choice and written answer, each with a worked explanation.
Vocabulary used: position, distance, displacement, scalar, vector, frame of reference.
Problem 1
Answer and explanation
25 km
The legs are perpendicular: displacement = √(7² + 24²) = √(49 + 576) = √625 = 25 km.
Problem 2
Answer and explanation
16 m
Distance is total path length: 10 + 6 = 16 m (the displacement, by contrast, is only 4 m east).
Problem 3
- speed
- distance
- time
- velocity
Answer and explanation
velocity
Velocity has both magnitude and direction, so it is a vector. Speed, distance, and time are scalars.
Problem 4
Answer and explanation
15 m
displacement = √(9² + 12²) = √(81 + 144) = √225 = 15 m.
Problem 5
- moving at 90 km/h
- accelerating steadily
- moving backward
- at rest
Answer and explanation
moving at 90 km/h
In the platform's frame of reference she is carried along with the train at 90 km/h, even though she is at rest in the train's frame.
Problem 6
Answer and explanation
A scalar has magnitude only — for example, a distance of 10 m or a speed of 5 m/s. A vector has both magnitude and direction — for example, a displacement of 10 m east or a velocity of 5 m/s north. Vectors need the direction stated to be fully described, and they combine using vector rules rather than simple addition.