# Braking a motorbike

How much distance would it take to stop a motorbike which has a mass of 210 kg, carrying an 80 kg rider, in dry conditions, travelling at 70 km/hr?

The answer will all depend on the size of the braking force which we do not appear to have! This force will depend on the brakes of the bike and the road conditions.

You say that we have a dry road so maybe we can compare it with a car although I really don't know how the brakes of a motorbike compare with those of a car as far as the stopping distance goes.

If we do assume that the brakes will produce a similar stopping distance to those of a car then at 70 km/hr the total stopping distance (thinking distance plus braking distance) would be about 44 m (thinking 13m plus braking 31m).

An alert and fit rider needs 0.75 of a second thinking time. That means that at 50 mph you'll travel 15 metres (about 50 feet) before you begin to brake.

The following table shows typical stopping distances

 Thinking distance Braking distance Stopping distance At 30 mph 9 metres(30 feet) 14 metres(45 feet) 23 metres(75 feet) At 50 mph 15 metres(50 feet) 38 metres(125 feet) 53 metres(175 feet) At 70 mph 21 metres(70 feet) 75 metres(245 feet) 96 metres(315 feet)

A VERSION IN WORD IS AVAILABLE ON THE SCHOOLPHYSICS CD