A sprinter's top speed is 10 m/s. Alongside the track, a car's dashboard shows 36 km/h. Which is faster? You cannot tell until both speeds speak the same unit.
Speeds arrive written both ways: a car's dashboard or a GPS app can show kilometers per hour, while physics works in meters per second. You've already seen how to convert kilometers to meters.
A speed in km/h says how many kilometers are covered in one hour. The same speed in m/s says how many meters are covered in one second.
Take a highway speed of 72 km/h. First fact: 72 km is 72 × 1000 = 72 000 m. Second fact: 1 hour is 60 minutes, and each minute is 60 seconds, so 1 hour is 60 × 60 = 3600 s.
So 72 km/h means 72 000 m covered in 3600 s. From earlier grades, speed = distance ÷ time. Divide: 72 000 ÷ 3600 = 20 m/s.
Now the opening question settles: the car's 36 km/h is 36 000 m in 3600 s, which is 10 m/s. A dead heat with the sprinter.
A highway bus travels at 90 km/h. What is the bus's speed in m/s?
Write down the values in the question:
speed = 90 km/h, wanted in m/s
Rebuild the conversion from its two facts:
90 km = 90 × 1000 = 90 000 m
1 h = 60 × 60 = 3600 s
So the bus covers 90 000 m in 3600 s. Divide:
90 000 ÷ 3600 = 25
The bus's speed is 25 m/s.
A delivery van drives at 54 km/h. What is the van's speed in m/s?
An express train passes a crossing at 108 km/h. What is the train's speed in m/s?
A cyclist rides at 12 m/s. What is the cyclist's speed in km/h?
Write down the values in the question:
speed = 12 m/s, wanted in km/h
Rebuild the conversion the other way:
In 1 h, which is 60 × 60 = 3600 s, the cyclist covers 12 × 3600 = 43 200 m.
Pack the meters into kilometers:
43 200 ÷ 1000 = 43.2
The cyclist's speed is 43.2 km/h.
A greyhound runs at 18 m/s. What is the greyhound's speed in km/h?
A high-speed train passes a platform at 144 km/h. What is the train's speed in m/s?
A stunt kite dives at 25 m/s. What is the kite's speed in km/h?
A scooter travels at 32.4 km/h. A runner's best pace is 11 m/s. By how many m/s is the runner faster than the scooter?