5
Review: motion problems
Textbook: Part 1, lesson 5, pp. 16–18
GoalReview the link between speed, time and distance and solve motion problems.
New words
speed · tezliktime · vaqtdistance · masofakilometres per hour · km/h
Explanation
With distance S, speed v and time t: S = v × t, v = S : t, t = S : v. If speed is in km/h, time is in hours and distance in kilometres; if speed is in m/min, time is in minutes and distance in metres. The units must match.
Worked examples
A cyclist riding at 15 km/h covers 15 × 4 = 60 km in 4 hours.
A train covers 360 km in 4 hours. Its speed is 360 : 4 = 90 km/h.
Class activity
“Walking speed”: in the school yard (with the teacher watching) a child measures how many metres they walk in 1 minute. The class then works out how far that is in 5 minutes.
Practice
1
A bus travelled for 5 hours at 60 km/h. How many km did it cover?
300
2
A car covers 288 km in 4 hours. What is its speed in km/h?
72
3
It is about 300 km from Tashkent to Samarkand. How many hours does a train going 75 km/h need?
4
4
The first cyclist rode 60 km in 4 hours, the second 84 km in 6 hours. Whose speed is greater?
The first: 15 km/h > 14 km/h