Speed, Distance, and Time
Lesson · Beginner
Algebra: Equations
A car travels 60 miles at 30 mph and another 60 miles at 60 mph. Find its average speed.
The total distance is 120
The times are
and
So the total time is 3
Therefore,
Notice that
Two runners start together on a 400-meter track and run in the same direction at 8 m/s and 6 m/s.
When will the faster runner first lap the slower runner?
The relative speed is 8 - 6 = 2 m/s
The faster runner must gain one full lap: 400 meters
Therefore,
Two trains of lengths 120 m and 180 m travel toward each other at 15 m/s and 10 m/s.
How long does it take them to completely pass each other?
They must cover a relative distance of 120 + 180 = 300 meters
Their relative speed is 15 + 10 = 25 m/s
Therefore,
Two towns are 240 miles apart. A car leaves the first town at 40 mph. At the same time, another car leaves the second town toward the first at 60 mph.
How far from the first town do they meet?
Their relative speed is 40 + 60 = 100
Thus the meeting time is
hours
The first car travels