1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Crash impact

  1. Sep 7, 2012 #1
    im new here and found your forum after using google i have a question relateing to a car accident after getting hit by a moped as the insurance company feels that the force could not have caused any damage hopefully someone here can help as it seems a very good forum.

    my wife was driving her car along a main road traveling at 30mph when a lorry traveling in the other direction swerved accross the road to avoid a bicycle as she is still a learner driver she panicked swerved away from the oncoming lorry and done an emergency stop at this point we felt a shunt forward and backward which was a moped which had hit us as she stopped then the front wheel hit the kerb making the backward forward motion.

    on speaking with the person after and accessing damage to both vehciles we exchanged details and left it to insurance companies to deal with however now they are saying it is a fraudulent claim and want to take me and my wife to court as i was the supervised driver what i would like to know is the following

    the moped weighs between 100-150 kgs the rider approx 70 kg i want to calculate when we was stationary what force would have been generated between the speeds of 20-30 mph as this has caused some damage to rear boot flooring pushing it up about half a centermetre and causing lower back problems however they seem to feel that it would not cause any of the following problems i am genuine and am not faking or misleading the other insurers in anyway and would like to know if someone can resolve my much needed question many thanks in advance and a great forum
  2. jcsd
  3. Sep 7, 2012 #2


    User Avatar
    Science Advisor
    Homework Helper

    We only have your version of the story, but the thing that doesn't make sense to me is what happened to the scooter rider - apparently nothing much.

    I know somebody who was in a stationary car (stupped at a red light) that was hit by a cyclist from behind at about 20 - 30 mph. The cyclist's excuse was that he didn't see the car because the weather was foggy!. The cyclist went right over the roof of the car and was taken to hospital with assorted broken bones. The only damage to the car was to the roof, where the cyclist hit it on the way over.

    If you claim your car was seriously damaged and the occupants got whiplash injuries but nothing much happend to the scooter rider, I'm not surprised the insurance company is asking questions.
  4. Sep 7, 2012 #3
    the bike had damage to the plastic paneling and the light was broken attached is a picture of the same model moped however not the one that hit the car but there saying the rider was not injured however he said he hit his legs on front panels on imapct and was rather sore

    but to me he hit the car so square that the bike took most of impact via the forks against the car as the damage to the car is exactally where the imapct was and i cannot see that this is just coincidence i will take phots of my car and post

    but want to know how much the weight is multiplied to when traveling at speed like a golf ball if you drop from a 1st floor block of flats onto something it wont cause as much damage as throwing from a 10 story high block of flats as speed and kinetic energy are going to play an important matter in the situation

    Attached Files:

  5. Sep 7, 2012 #4
    inside boot floor

    although its hard to see in light there are stress marks across the bumper where impact was the wheel and mudguard to bike went under the bumper pushing the car up in the air and assuming it then pushed the spare wheel upwards resulting in the inner floor pan pushing upwards
    the trim is cracked around the lock along with a bullet like small dent which i feel is down to the such pointed front above the forks of the bike

    underneath of car where spare wheel is has been pushed back and back supporting welds broken giving me the impression that the front wheel of moped is 13 inches with out tyre =14-15 inches has hit underneath of car causing bolt that holds wheel in carraige to be pushed forward resulting in the floor being bent upwards and at that point the moped front wheel wedged underneath the car and then stopped the bike being flung forward due to the front pointy panel against the boot causing the bullet like dent now all i need to know is what the estimated weight would have been of him hitting the car under the estimated speed.

    although people seem to think it wouldnt do that if the front corner hit a centre rear of car pulling out a junction it often makes a v shape in the back of car if the damage had been previously caused by a car it would be distributed via the rear slam panel rather than from the spare wheel getting pushed up which is why the damage is only to a limited area as the moped is only a small width unlike a car has anyone got anything they can add to this or answer the question of what impact force could have been generated

    Attached Files:

    Last edited: Sep 7, 2012
  6. Sep 8, 2012 #5
    KE won't help here. If the rider came to a dead stop in an amount of time you can guess (500 ms?) from a speed you can guess (25mph), than F=ma should give you an estimate.

    While motorcycles generally don't have enough mass to actually hurt vehicle occupants, they can certainly damage body panels on vehicles.
  7. Sep 8, 2012 #6
    I think the main Problem thats caused my injurie is im quite tall so have the seat right back i was lent forward getting something out my glovebox when the impact happened causeing me to jolt back then as our front wheel hit the kerb i went forward a little which happened so quick but jolted my neck which has then caused minor injuries to my neck and centre of my back ive been examined by a medical expert that says my muscles are quite tight and tense in my back and its caused from the accident im wondering if there may have been problems with my neck and back and this may have brought them to light
  8. Sep 8, 2012 #7
    Forgot to ask
    So someone whos clever to calculate a starting weight of 180kg slowing from 30mph to 25mph on impact im not stupid on many things but calculateing things like this is well over my head
  9. Sep 10, 2012 #8
    Taking a stab at it.

    F = ma
    Mass = 180 kg
    acceleration = change in speed over change in time
    v = 30 mph = 13.41 meter/sec
    ~t = 500 ms = 0.5 s

    so acceleration = 13.41 m/s /5 ms = 26.28m/s^2

    So the force the little scooter hit you was
    F=180kg * 26.28m/s^2
    F = 4730.4 N

    Is that enough to damage your bumper?
  10. Sep 11, 2012 #9
    Have you considered that maybe the swerve and emergency stop jolted you around a bit?
    You'd pull more G's in a maneuver like that than you would being struck in the bumper by a moped which was almost certainly not going 20 mph when it actually hit you (as you say, the moped was in the process of stopping).

    Does the moped/person have enough mass to give you a bump? Yea, probably.
    Enough to cause whiplash without the driver being ejected or being slammed into the car's rear end? I doubt it.
  11. Sep 11, 2012 #10


    User Avatar
    Science Advisor
    Homework Helper

    That's almost certainly too simple to be useful. For example, it says the distance travelled by the scooter during the 0.5 s impact = (1/2) a t^2 = 3.35 meters, which doesn't make much sense.
  12. Sep 11, 2012 #11
    The rider said he was going 30mph and his brakes didnt work as it was a chinesse import and that he had no money to get fixed the thing is was he useing that as an excuse because he failed to see us stopping i will never know only he will everyone knows what mopeds are like flys up behind people tailgates and so on with basically no road knowledge needed to ride one they should make all cbt riders take a theroy test before being allowed on the roads
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook