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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
878099 2010-04-19 09:34:00 Force = change in impulse divided by change in time. ([velocity final - velocity initial] over [time final - time initial])

So the force is what you're after. (Weight is not equal to mass.)

Let's see... Assuming it stops, (360 - 0) / (tf - ti) {100km/h = 360 metres per second}

We still need to know how quickly it stopped.

Motorcycle into police car.

I'd assume motorcycle and rider deflected off and traveled an unknown distance (bike would have been destroyed so it wouldn't be a huge distance), The police car was spun.

The question was just to ascertain if the bike traveling at road legal speeds would hit with enough force to shunt a car.... 		Metla (12)
878100 2010-04-19 09:38:00 I'll assume half a second to stop, but a precise value will help. :)

So carrying on, 360 / (0.5 - 0)
=360/0.5
=720N
=72kg

Hope I got it right :p 		pcuser42 (130)
878101 2010-04-19 09:42:00 Well I have seen a racehorse kick a car in the side and shunt one end of it sideways about 45° gary67 (56)
878102 2010-04-19 10:38:00 I'll assume half a second to stop, but a precise value will help. :)

So carrying on, 360 / (0.5 - 0)
=360/0.5
=720N
=72kg

Hope I got it right :p

You're a factor of 30 out: you forgot the mass & converted to m/s wrong.

100kph = 36m/s, so

As Jamuz said before, Force = (change in momentum)/time, so if we keep assuming that the bike just comes to a complete stop in 0.5s, then

F = ((36*300) - (0*300))/0.5
=21600N, or roughly equivalent to a weight of 2200kg

... the car would definitely move, I'd say ;) 		MushHead (10626)
878103 2010-04-19 10:53:00 I thought the title said 'quick' physics question? pine-o-cleen (2955)
878104 2010-04-19 11:46:00 Don't forget to factor into the equation the inertia (in the direction the bike hit it) the car would have had at the time of impact. Plus the friction of the car tyres on the road. But since the car was doing a u-turn, and therefore moving, albeit at a lowish speed, the tyre friction would have been less than if it were stationary.

And the fact the I would assume the rider (at approximately 100kg), would have been separated from his bike (the other 200kg) shortly after impact. Whereas the bike would have continued shedding momentum on the side of the police car for several more moments.

So as pine-o-cleen so rightly pointed out, a "quick physics question?"!!!

I don't think there's an easy answer to this one. I wonder if Mythbusters could recreate it for us? 		johcar (6283)
878105 2010-04-19 11:47:00 Motorcycle into police car.

I'd assume motorcycle and rider deflected off and traveled an unknown distance (bike would have been destroyed so it wouldn't be a huge distance), The police car was spun.

The question was just to ascertain if the bike traveling at road legal speeds would hit with enough force to shunt a car....

just watched it on the news.
it dosn't take a lot to shunt a car sideways. hitting at the rear by the looks of it, bit of leverage effect, its effectively only pushing on half a car.
even tho it looses a fair bit of force as the rider comes off, even a 50km/h impact would shunt a car.

tho it looks like a @#$ of a place to do a U turn :mad: 		tweak'e (69)
878106 2010-04-19 20:15:00 No one was present,so let the conjecture begin....... Cicero (40)
878107 2010-04-19 20:46:00 No one was present,so let the conjecture begin.......

Yes there was, 1 police officer, and one dead dude (got that from bill and ted :)) 		Gobe1 (6290)
878108 2010-04-19 20:50:00 you forgot the mass & converted to m/s wrong.

100kph = 36m/s

Oops, multiplied by 3.6 instead of divided :blush:

Still, 100km/h = 27.78m/s. 		pcuser42 (130)
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