46
Distance, time and speed
Textbook: Part 2, lesson 46, pp. 22–24
GoalDistance, time and speed: the formulas S = v × t.
New words
speed · tezlikdistance · yo‘l (masofa)time · vaqtuniform motion · bir tekis harakat
Explanation
In uniform motion distance S, speed v and time t are linked: S = v × t. From this v = S : t and t = S : v. Speed is measured in km/h, m/min or m/s. For example, a car at 80 km/h for 3 h covers S = 80 × 3 = 240 km. A cyclist who covers 45 km in 3 h has speed 45 : 3 = 15 km/h.
Worked examples
v = 80 km/h, t = 3 h: S = 80 × 3 = 240 km.
S = 20 km, v = 5 km/h: t = 20 : 5 = 4 h.
Class activity
“Formula triangle”: write S on top and v and t below; cover one letter and show how to find it.
Practice
1
A car travelled at 70 km/h for 4 h. How many km did it cover?
280
2
A train covered 300 km in 3 h. What was its speed in km/h?
100
3
How many hours does a walker at 5 km/h need for 20 km?
4
4
A boat moved at 2 m/s for 50 s. How many m did it cover?
100