Like a buffalo, horse or giraffe hitting your car
TO understand the brute force of rocks falling on cars, the following velocity and impacts were estimated and compared.
Bridge height: 5m
Speed of car: 120km/h Weight of rocks: can vary significantly, anything from 3kg to 20kg seems reasonable.
Additional data also involved in equation.
Data is assumed under general circumstances and the projectile being dropped and not thrown.
A 3kg rock dropped from a 5m high bridge on a car travelling at 120km/h is equal to the impact of a 183kg weight dropped from a height of 1m, which is equivalent to the weight of a small piano.
A 9kg rock dropped from a 5m bridge would impact a car with the same amount of energy as a 549kg mass being dropped from 1m.
This is roughly the weight of a buffalo.
A 15kg rock dropped from a 5m bridge would impact a car with the same amount of energy as a 549kg mass being dropped from 1m. This is roughly the weight of a horse.
A 20kg rock dropped under the same conditions is equivalent to dropping 1 219kg from 1m. This is approximately the weight of a giraffe.
Energy values for different rock masses
Mass of rock = Equivalent mass dropped from 1m height
3kg = 183 kg
5kg = 305kg
7kg = 427kg
9kg = 548kg
11kg = 670kg
12kg = 731kg
15kg = 914 kg
20kg = 1219kg
Data supplied by Shamik Maharaj, a masters quantum physics student at the University of KwaZuluNatal.