44
Moving a point along the number ray
Textbook: Part 2, lesson 44, pp. 16–18
GoalA point moving along the number ray: find its coordinate.
New words
movement · harakatto the right · o‘ng tomongato the left · chap tomongaevery second · har sekundda
Explanation
If a point moves evenly along a ray, it covers the same distance every second. Moving right, the coordinate increases: new coordinate = start + speed × time. Moving left it decreases: start − speed × time. For example, from 3 moving right 2 unit segments per second for 5 s gives 3 + 2 × 5 = 13. To find the time: (end − start) : speed.
Worked examples
Start 5, to the right at 3 e per second for 4 s: 5 + 3 × 4 = 17.
Start 30, to the left at 4 e per second for 6 s: 30 − 4 × 6 = 6.
Class activity
“Living ray”: children walk step by step along a line marked on the classroom floor from 0 to 10 (nothing hazardous in the way) to the coordinate a classmate calls out.
Practice
1
A point starts at coordinate 5 and moves right at 3 unit segments per second for 4 s. What is its new coordinate?
17
2
A point starts at coordinate 30 and moves left at 4 unit segments per second for 6 s. What is its new coordinate?
6
3
A point at coordinate 2 moves right at 5 unit segments per second. After how many seconds does it reach coordinate 27?
5
4
A point at coordinate 40 moves left at 3 unit segments per second. After how many seconds does it reach coordinate 4?
12