The braking distance of a road train travelling at 15m/s is 70m. Assuming that the same braking force is applied at all speeds, show that the braking distance of a road train when travelling at 25m/s is about 190m.

Energy = force x distance and Energy = 0.5 x mass x velocity squared

Hence, force = (0.5 x mass x velocity squared) / distance --- (equation 1) This applies for both situation A and B, and given that force is stated to be the same in each case, and mass is the same, we can equate eqn 1 for each.

Hence, (0.5 x mass x velocity(A) squared) / distance(A) = (0.5 x mass x velocity(B) squared) / distance(B)

and so distance(B) = (velocity(B) squared x distance(A)) / (velocity(A) squared) = (25^2 x 70) / 15^2 = 194m