Time, speed and distance

Key ideas

• Distance = speed × time.
• km/h to m/s: multiply by 5/18; m/s to km/h: multiply by 18/5.
• Average speed for equal distances at speeds a and b = 2ab/(a + b).
• A train crossing a pole covers its own length; crossing a platform covers its length plus the platform’s.
• Boats: downstream speed = boat + stream; upstream = boat − stream.