If x km/h = y m/s, then y =

Analyze the question: We need to convert a speed from km/h to m/s and express y in terms of x.

Concept:

• 1 km = 1000 m
• 1 hour = 3600 seconds

Solution:

x km/h = x × (1000 m) / (3600 s)

= x × (1000/3600) m/s

= x × (5/18) m/s

So y = (5/18)x.

Check with a number: 36 km/h = 36 × 5/18 = 10 m/s. Since 36 km/h is 36000 m in 3600 s, which is 10 m/s, this is correct.

Answer: Option D, y = (5/18)x.

Tip: To convert km/h to m/s, multiply by 5/18. To convert m/s to km/h, multiply by 18/5. A quick reminder: "km/h to m/s, go smaller, so multiply by 5 over 18."