118
Distance, time and speed
Textbook: Part 4, lesson 118, pp. 25–27
GoalThe link between distance, time and speed: s = v × t, v = s : t, t = s : v.
New words
distance · yo‘l (masofa)time · vaqtspeed · tezlikformula · formula
Explanation
Movement problems have three quantities: distance s, time t and speed v. Distance = speed × time: s = v × t. Speed = distance : time: v = s : t. Time = distance : speed: t = s : v. The units must match: km/h goes with km and hours, m/min goes with m and minutes.
Worked examples
If v = 60 km/h and t = 3 h, then s = 60 × 3 = 180 km.
If s = 360 m and v = 45 m/min, then t = 360 : 45 = 8 minutes.
Class activity
“Formula triangle”: children write s, v and t in a triangle (s on top, v and t below) and, covering one letter, say which operation finds it.
Practice
1
A car drove at 70 km/h for 4 hours. How many km did it cover?
280
2
In how many hours does a cyclist riding at 15 km/h cover 90 km?
6
3
A bee flew at 6 m/s for 20 seconds. How many m did it cover?
120
4
In how many minutes does a walker going 60 m/min cover 1 800 m?
30