MHB Help Needed: Calculating Speed After Motorcycle Accident

[bikerguy]

Hi there Ladies and Gentlemen. My name is Andre, and I am from South Africa and would like if someone could assist me.
Im going to admit that maths is not my forte and I am lost when it comes to anything more than plus or minus or times. lol
I was in a motorcycle accident recently , and after spending months in hospital, I now face the Court cases. I would like someone to help in finding one thing: What speed was I traveling upon collision?

Point of impact to where I came to contact with tarmac, is 12m
height of launch point is 1.2m above contact point
I weigh 109 kilograms
i rolled another 3m
Launch angle is between 10 to 20 degrees, although, this is the general estimate found on the internet.

if anyone can help, it would be appreciated, as i cannot afford an attorney, and I will have to make my own representation in court.

Thank You!

 

[Ackbach]

It would greatly help the analysis if you could please post a picture or drawing of the physical situation, with labels for everything you know.

 

[bikerguy]

It would greatly help the analysis if you could please post a picture or drawing of the physical situation, with labels for everything you know.

HI Ackbach, here is what i know
View attachment 4703

 

[topsquark]

I've done a couple of checks on this and the only thing I can think of is that your numbers are inconsistent.

The sliding part is pretty decent. I couldn't get any sort of "rolling friction" data so I had to assume that the rider is sliding. This would imply a speed greater than that predicted by rolling, but I can't say by how much. Anyway the estimate of the horizontal component of the velocity at impact will be [math]\sqrt{6 \mu _s g} \approx 6.859~\text{ m/s}[/math] using a hybrid guess of [math]\mu _s = 0.8[/math]. The guess comes from an eyeball judgement of 4 different surface combinations that I thought were relevant.

So far so good. Now for the projectile part of the motion. To do this properly the initial vertical motion is caused by a rotation of the motorcycle at the point of impact with the truck. I need the horizontal distance from the back of the truck to where the rider is sitting and the vertical distance from the back of the truck to how high the rider was sitting. Without this information we have to confine ourselves to a consistency check on the speed found from the sliding part of the motion.

Again we are missing data. The simplest way to continue here is to assume that h is about 1.5 m. But that is where this all goes to Hades. I'm taking the horizontal component of the velocity at the point of impact to be our previously calculated 6.859 m/s and we need to find an initial vertical component of velocity. This comes in at more than 19.795 m/s, which implies an angle some 70 degrees. But this angle has to be less than the 15 degrees you are estimating.

The only conclusion I can draw is that the speed the motorcycle hits the truck with is significantly greater than the predicted 6.859 m/s (15.3 mph). Without more consistent data that's all I can say.

-Dan

 

[bikerguy]

I've done a couple of checks on this and the only thing I can think of is that your numbers are inconsistent.

The sliding part is pretty decent. I couldn't get any sort of "rolling friction" data so I had to assume that the rider is sliding. This would imply a speed greater than that predicted by rolling, but I can't say by how much. Anyway the estimate of the horizontal component of the velocity at impact will be [math]\sqrt{6 \mu _s g} \approx 6.859~\text{ m/s}[/math] using a hybrid guess of [math]\mu _s = 0.8[/math]. The guess comes from an eyeball judgement of 4 different surface combinations that I thought were relevant.

So far so good. Now for the projectile part of the motion. To do this properly the initial vertical motion is caused by a rotation of the motorcycle at the point of impact with the truck. I need the horizontal distance from the back of the truck to where the rider is sitting and the vertical distance from the back of the truck to how high the rider was sitting. Without this information we have to confine ourselves to a consistency check on the speed found from the sliding part of the motion.

Again we are missing data. The simplest way to continue here is to assume that h is about 1.5 m. But that is where this all goes to Hades. I'm taking the horizontal component of the velocity at the point of impact to be our previously calculated 6.859 m/s and we need to find an initial vertical component of velocity. This comes in at more than 19.795 m/s, which implies an angle some 70 degrees. But this angle has to be less than the 15 degrees you are estimating.

The only conclusion I can draw is that the speed the motorcycle hits the truck with is significantly greater than the predicted 6.859 m/s (15.3 mph). Without more consistent data that's all I can say.

-Dan

Thank You Dan,
Perhaps this can help?

Studies show that the coefficient of friction between the operator’s clothing and the roadway surface for cotton/ wool and polyester is between .7 to .85 g’s and for leather is between .6 to .7 g’s. When a body does not slide but tumbles the coefficient of friction is approximately 1.0 or higher. There may be a combination of sliding and tumbling so the slide to stop coefficient of friction may vary

View attachment 4712