robb

I need help with an accident law suit I'm working on.

Do any of you know the formula for calculating the acceleration of an object when struck by another object.

Object A (mass 4,135 lbs) strikes object B (mass of 6,485 lbs) currently traveling at 10 mph.

I need to figure the required velocity of object A to accelerate object b from 10 to 30+ MPH. For ease we can assume a negligable coeeficient of friction for the objects....

Any help would be great...

And remember "Physics is Phun!"

psoper

you are thinking of this as being a conservation of momentum problem, in which case momentum is m*v and is conserved provided their isn't energy being added to the system.

So there are two variables for each vehicle in both the initial condition and after the impact.
Ma1 and Va1, as well as Mb1 and Vb1 before the impact and Ma2 and Va2, as well as Mb2 and Vb2 after

ie; 4135*Va1 + 6485*10 should roughly equal 4135 Va2 + 6485*30

But that leaves us one equation with 2 variables, which can't be solved;
you don't say what the speed of object A is after the impact, that is pretty much the missing piece of the puzzle.

robb

Pretty much stopped....so <5. or 0 would suffice.

ish

iTrader: (7)

without going home to look at my old text books

off the top of my head this is waht i come up with.

assuming no external input of energy and no dissipation of energy and no surface friction, and there is convservation of momentum.

momentum of object A + B before collision should equal the momentum of object B after the collision (since A is not moving after collision)

we will not momentum as "p", velocity as "v" and mass as "m"

p = m*v

due to conservation of momentum: p1 = p2

p1 = (mA*vA1) + (mB*vB1)
and
p2 = mB*vB2

so

(mA*vA1) + (mB*vB1) = mB*vB2

since everything is linear you can get rid of the directional aspect of p and v and label them as p and v respectivly

now just insert your known variables and solve and you get your initial speed of object A (v1)

vA1 = 31.37 mph



note: this is not accurate. i am assuming this is two cars running into each other. friction exists, especially if object B applies its breaks and on impact of the two, energy is dissipated due to damamged car parts and stuff. above is assuming no damage was caused to either car. actual speed of object A would need to be faster.

mexicanpizza

iTrader: (9)

You can't calculate it remotely accurately without taking into account the deformation/crushing of the recipient car.

Sorry to hear about your accident.

robb

I guess I didnt explain what happened in the first post...lol this is an old accident but it is on the legal phases now.

I was dead stopped 4-5' behind a car on I-210 in LA. A Chevy Avalance rearended me into the car in front of me.

I saw him coming at a high rate of speed, hear his brakes screeching, and then wham....I got hit into the car in front of me.

I estimated his speed upon impact to eb 30 MPH. He is denying my claim stating that he was hit into me by a sedab and was only doing 10 MPH.

Well I am thinking for a sedan to accelerate a Chevy Avalance from 10 to 30 while on the brakes would have had to have been going 70-80 MPH.

ish

iTrader: (7)

let me see if i am reading this right.

so was there a forth car involved? cause if he claims he was hit into you where is that damaged car and his rear end damage?

or did i read that wrong?

robb

No you read it correctly...

Thats why I'm taking him to court. He had ZERO damage to the rear of his truck...the dirt wasnt even knocked off the bumper...and he claims it wa sa hit and run....well all 6 lanes were dead stopped so I dont know where the tank that hit him went....because if it were a car that hit him that hard....I knwo I would have seen it spewing coolant and dragging the front end on the way by...

verc

iTrader: (12)

bwahahaha you tell 'em.
*tsk tsk* algebra-based physics doesn't really cut it when calculating the real world

verc

iTrader: (12)

o yeah, Sorry to hear about your accident. Moving SUV's are bad. He might well have been going like 15 mph since he probably weighs 3 times as much as has thrice the momentum as you