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Thread ID: 108982	2010-04-19 07:25:00	Quick question, Physics?	Metla (12)	PC World Chat

Post ID	Timestamp	Content	User
878139	2010-04-22 01:41:00	Hi Metla. re: 300kg mass, traveling at 100km/h, if it hit an object what would its weight register at? Would the formula change if the 300kg mass was following (possibly attracted by) a 2 tonne mass travelling in the same direction and slightly ahead of it?	Scouse (83)
878140	2010-04-22 03:12:00	What about speeding on bike can cause death. I have lost 2 mates in bike accidents although one was pissed and speeding. :illogical Thats akin to saying crossing the road can cause death. Utterly meaningless, The act itself doesn't kill people, doing it stupidly or beyond your capabilities is another matter entirely. Someone else doing something that kills you why your going about your business is an entirely different matter.	Metla (12)
878141	2010-04-22 03:15:00	Hi Metla. re: 300kg mass, traveling at 100km/h, if it hit an object what would its weight register at? Would the formula change if the 300kg mass was following (possibly attracted by) a 2 tonne mass travelling in the same direction and slightly ahead of it? If you inserted 10 trucks into the equation would it make any difference? The truck has no bearing on the course of events. If the police officer has such poor judgement that he would cause a death of a person over a potential ticket then it was only a matter of time.	Metla (12)
878142	2010-04-22 03:23:00	Given the extensive calculations, is this related to the plane on a treadmill question? No, it's just that no one knows how to do it :p	pcuser42 (130)
878143	2010-04-22 04:42:00	At last count, this quick (yeah right) physics question has been on for 4 days, been viewed by 1,029 and received 53 replies ... of which only 10% have given a "reasonable" answer or information in an attempt to solve the original problem. Priceless !!	SP8's (9836)
878144	2010-04-22 04:43:00	That's physicists for ya :p	pcuser42 (130)
878145	2010-04-23 01:35:00	Without more information (namely the time duration of the crash) we can't answer the actual question you intended to ask . However, if we assume the motorbike rider was princess diana then: . info/acceleration/" target="_blank">physics . info this has the useful number of 70-100g acceleration experienced in her fatal crash . Of course Diana was probably going faster than 100kph . Another useful number for force I found was fatal limits of 15-45g depending on orientation . Since this guy died, it was probably > 15 . If you can find a more useful acceleration number use that instead . I didn't google for long . A 300kg motorbike decelerating at 30g produces a force (this is the 'weight' you asked for) of 88kN . Now, the second part of your question: could this 'spin' a police car? Let's assume that the bike hit the car side on in line with an axle . The coefficient of a tire on concrete is 1 . 7, and the weight of the car over that axle is about 7kN, so it would need a force of about 12kN to move it . 88>12 so yes, although this is highly dependant on the g force assumed in the collision .	shermo (12739)
878146	2010-04-23 01:43:00	That answer sucks, so here's a better way to approach it . Assume inelastic collision (note that we know this is NOT the case, but it makes things calculable) . Also, assume that since the bike hit the car off its centre of mass we can halve the mass of the car (also NOT true, but in the absence of knowing exactly where the bike hit the car it's a good guess) Momentum before collision = momentum after collision . Mbc = 300*28 = 8400kgms Mac = 1000*x = 8400kgms (half a 1500kg car) velocity after collision = 8400/1000 = 30 . 24kph . Let's bypass all the impulse, coefficient of friction stuff . If you're driving at 30 . 24kph and lock your tires, do your tires skid? Probably So this is consistent with the answer above . Yes, if the bike was doing 100k it could spin a police car .	shermo (12739)
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