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skellator
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Location:
Coffs Harbour, NSW
Registered:
November 2004

Re: Physics problem.

Thu, 24 March 2005 05:57

ok, where to start...

right, so, if you cut it down to the basics, the impact of two exactly the same cars travelling in exactly opposite directions at 50km/h would be the same as if one car hit a solid wall at 100km/h.
but, of course, the wall is not the same as a car. the cars are made of easily shape changing metal (or plastic)

Quote:

As for the original question, if two cars travelling at 50km/h collide head-on the impact will be the same as one car travelling at 50km/h hitting a solid object (eg concrete wall). In other words, hitting another car at the same speed is the same as hitting a solid object.

this is definetely incorrect, have a think about the relative speeds involved for the cars: to car 1, car 2 is travelling at 100km/h

Quote:

Potential energy of the cars;

PE = 0.5*m*V^2

i belive you mean kinetic energy, KE, here?
KE = 1/2m.v^2
PE = m.g.h

to solve this problem, we need to consider the velocity of one car relative to the other. by using vectors (i cant draw them here), we can conclude that car 2 is travelling at 100km/h relative to car 1, and vice versa. note that this is assuming they are travelling at exactly the same velocity (50km/h, opposite direction), ignoring air resistance, and that they are exactly the same car, with the same weight, and no acceleration until the moment of impact (no acceleration or deceleration or change of direction)
assuming the mass of each car is, say, 1000kg, both car's initial velocity is 14m/s (50km/h = 13.9m/s) in opposite directions, the final velocity is 0m/s for both cars, and the time taken for the whole process is 0.5s, we can use newton's 2nd law to find the force exerted on each car:
F = (m.v - m.u)/t
= (1000x14 - 1000x0)/0.5
= 14000/0.5
= 28000 N

for the impact with the wall (assuming it will not move at all), however, the time will be much less, due to the fact that only the car has collapsible parts, where the wall does not, whereas in the collision between two cars, both objects are able to change shape. therefore, we will assume the time for the collision with the wall to be 0.1s. so the force on the car:
F = (m.v - m.u)/t
= (1000x14 - 1000x0)/0.1
= 14000/0.1
= 140000 N

as you can see, the force for the impact with the concrete wall would be much higher than for a collision between two cars

jeez, that would have to be my longest post ever! i hope to never have to do it again Razz

[Updated on: Thu, 24 March 2005 06:29]

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Read Message Physics problem. Squid Thu, 24 March 2005 03:43
Re: Physics problem. Corona RT142 Thu, 24 March 2005 03:46
Re: Physics problem. Squid Thu, 24 March 2005 03:50
Re: Physics problem. Corona RT142 Thu, 24 March 2005 03:50
Re: Physics problem. Norbie Thu, 24 March 2005 03:51
Read Message Re: Physics problem. Squid Thu, 24 March 2005 03:58
Re: Physics problem. Indi Thu, 24 March 2005 04:28
Re: Physics problem. STR8 2.8 Thu, 24 March 2005 04:32
Re: Physics problem. 86DRFT Thu, 24 March 2005 12:27
Re: Physics problem. Norbie Fri, 25 March 2005 07:14
Read Message Re: Physics problem. Intensevil Thu, 24 March 2005 04:25
Re: Physics problem. Corona RT142 Thu, 24 March 2005 04:31
Re: Physics problem. Squid Thu, 24 March 2005 04:34
Re: Physics problem. Indi Thu, 24 March 2005 04:42
Re: Physics problem. BlackMR2 Thu, 24 March 2005 04:32
Read Message Re: Physics problem. white86 Thu, 24 March 2005 04:44
Re: Physics problem. white86 Thu, 24 March 2005 04:51
Re: Physics problem. Mookie Thu, 24 March 2005 04:58
Re: Physics problem. bbaacchhyy Thu, 24 March 2005 05:08
Re: Physics problem. IRA11Y Thu, 24 March 2005 05:39
Read Message Re: Physics problem. Dust Thu, 24 March 2005 05:34
Re: Physics problem. Norbie Thu, 24 March 2005 05:39
Re: Physics problem. skellator Thu, 24 March 2005 05:57
Re: Physics problem. BlackMR2 Thu, 24 March 2005 05:58
Re: Physics problem. IRA11Y Thu, 24 March 2005 06:04
Read Message Re: Physics problem. IRA11Y Thu, 24 March 2005 06:07
Re: Physics problem. EnFlaMEd Thu, 24 March 2005 06:33
Re: Physics problem. SPRINTAH! Thu, 24 March 2005 06:30
Re: Physics problem. skellator Thu, 24 March 2005 06:43
Re: Physics problem. SPRINTAH! Thu, 24 March 2005 07:47
Read Message Re: Physics problem. IRA11Y Thu, 24 March 2005 08:13
Re: Physics problem. skellator Thu, 24 March 2005 08:57
Re: Physics problem. skellator Thu, 24 March 2005 06:33
Re: Physics problem. RWDboy Thu, 24 March 2005 06:42
Re: Physics problem. skellator Thu, 24 March 2005 06:54
Read Message Re: Physics problem. RWDboy Thu, 24 March 2005 06:49
Re: Physics problem. RWDboy Thu, 24 March 2005 07:20
Re: Physics problem. skellator Thu, 24 March 2005 07:44
Re: Physics problem. RWDboy Thu, 24 March 2005 13:42
Re: Physics problem. CrUZsida Thu, 24 March 2005 08:39
Read Message Re: Physics problem. CrUZsida Thu, 24 March 2005 08:59
Re: Physics problem. NeiGH Thu, 24 March 2005 09:51
Re: Physics problem. skellator Thu, 24 March 2005 10:01
Re: Physics problem. Alex120 Fri, 25 March 2005 11:49
Re: Physics problem. 86DRFT Thu, 24 March 2005 12:22
Read Message Re: Physics problem. skellator Fri, 25 March 2005 01:42
Re: Physics problem. RWDboy Fri, 25 March 2005 08:16
Re: Physics problem. b1gb3n Fri, 25 March 2005 02:37
Re: Physics problem. skellator Fri, 25 March 2005 08:40
Re: Physics problem. RWDboy Fri, 25 March 2005 09:10
Read Message Re: Physics problem. skellator Fri, 25 March 2005 09:22
Re: Physics problem. gabe Sat, 26 March 2005 00:46
Re: Physics problem. skellator Sat, 26 March 2005 00:58
Re: Physics problem. RobertoX Wed, 30 March 2005 05:40
Re: Physics problem. skellator Wed, 30 March 2005 06:35
Read Message Re: Physics problem. RWDboy Fri, 25 March 2005 10:42
Re: Physics problem. Alex120 Fri, 25 March 2005 11:45
Re: Physics problem. RWDboy Fri, 25 March 2005 12:40
Re: Physics problem. skellator Fri, 25 March 2005 22:50
Re: Physics problem. RWDboy Sat, 26 March 2005 01:47
Read Message Re: Physics problem. skellator Sat, 26 March 2005 02:16
Re: Physics problem. gabe Sat, 26 March 2005 02:59
Re: Physics problem. RWDboy Sat, 26 March 2005 01:53
Re: Physics problem. RWDboy Sat, 26 March 2005 03:21
Re: Physics problem. IRA11Y Sat, 26 March 2005 03:29
Read Message Re: Physics problem. Squid Tue, 29 March 2005 03:48
Re: Physics problem. RWDboy Sat, 26 March 2005 03:29
Re: Physics problem. RWDboy Sat, 26 March 2005 03:33
Re: Physics problem. skellator Sat, 26 March 2005 03:41
Re: Physics problem. RWDboy Sat, 26 March 2005 04:13
Read Message Re: Physics problem. skellator Sat, 26 March 2005 04:24
Re: Physics problem. RWDboy Sat, 26 March 2005 04:47
Re: Physics problem. IRA11Y Sat, 26 March 2005 05:04
Re: Physics problem. skellator Sat, 26 March 2005 05:26
Re: Physics problem. skellator Sat, 26 March 2005 06:06
Read Message Re: Physics problem. tom210 Sat, 26 March 2005 06:52
Re: Physics problem. skellator Sat, 26 March 2005 06:56
Re: Physics problem. RWDboy Sat, 26 March 2005 07:02
Re: Physics problem. skellator Sat, 26 March 2005 07:05
Re: Physics problem. tom210 Sat, 26 March 2005 07:19
Read Message Re: Physics problem. jackel Sat, 26 March 2005 07:23
Re: Physics problem. skellator Sat, 26 March 2005 07:39
Re: Physics problem. tom210 Sat, 26 March 2005 07:28
Re: Physics problem. Norbie Sat, 26 March 2005 09:47
Re: Physics problem. skellator Sat, 26 March 2005 10:10
Read Message Re: Physics problem. Norbie Sat, 26 March 2005 10:12
Re: Physics problem. skellator Sat, 26 March 2005 10:21
Re: Physics problem. EldarO Sat, 26 March 2005 11:37
Re: Physics problem. Norbie Sun, 27 March 2005 02:02
Re: Physics problem. EldarO Tue, 29 March 2005 16:41
Read Message Re: Physics problem. tom210 Sat, 26 March 2005 12:46
Re: Physics problem. RWDboy Sat, 26 March 2005 12:53
Re: Physics problem. skellator Sun, 27 March 2005 02:36
Re: Physics problem. RWDboy Sun, 27 March 2005 03:15
Re: Physics problem. RWDboy Tue, 29 March 2005 04:41
Read Message Re: Physics problem. skellator Tue, 29 March 2005 05:50
Re: Physics problem. RWDboy Tue, 29 March 2005 12:07
Re: Physics problem. skellator Tue, 29 March 2005 21:05
Re: Physics problem. 79rollaboy Tue, 29 March 2005 21:20
Re: Physics problem. RobertoX Wed, 30 March 2005 00:19
Read Message Re: Physics problem. RWDboy Wed, 30 March 2005 00:42
Re: Physics problem. skellator Wed, 30 March 2005 04:40
Re: Physics problem. RobertoX Wed, 30 March 2005 04:49
Re: Physics problem. skellator Wed, 30 March 2005 04:57
Re: Physics problem. RWDboy Wed, 30 March 2005 13:47

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