Brain Teaser

[Space Ace]

It is a trick question as you cannot manually switch the engine off if the car is travelling....

[nang3]

yeh but surely if you are accelerating rapidly to 100kph, when you switch the engine off in the accelerating car, there will still be some residual acclerative inertia to cause the 2nd car to actually go past 100kph, even if to only 105kph, whereas the car already at 100 will instantly start slowing down the second the engine is switched off...

actually the more I think about it the more im not sure, im going to test it out later hhehehehe.. anything to get out of work for a few mins hehe

[ExAreSix]

Bah, nevermind...

[Honest Gaza]

  TurboDewd said:

F6 Rapid and 4runner are correct.

AT the moment the engines are switched off no more force is causing either vehicle to move.  Newton's first law of motion applies:

I. Every object in a state of uniform motion tends to remain in that state of motion unless an external force is applied to it.

Each car had a force being applied to it (the engine) and that force stopped, they would then uniformly slow to a complete stop since the effects of air resistance and friction slow the cars down.

I'm not saying I am corect...but I disagree with your answer.

Force = Mass x Acceleration.....and therefore, the Forces would be different due to the diferences in Acceleration. (This was argued in an earlier thread when discussing the merits of having better brakes for those cars that have the ability to accelerate quickly. While some said a car doing 100kmh will need the same braking power as any other car doing the same speed, and weighing the same, others argued that whichever car accelerated fastest would require additional brake power appeared valid)

Someone who knows much more than me can tell me if I am full of it.

[Blonk]

True - The second car is travelling under acceleration so if it is switched off at the exact moment it hits 100 it will travel above 100 until the forces of air resistance and friction casue it to slow...

I.E.

Car 1

The car travelling at 100 (lets say its a Expensive Daewoo cause 100 is stalling speed for a ford) =

F = ma

F = ?

m = 1600kg

a = 0 as car is travelling at constant 100kmh (vu = 100 , v = 100)

Therefore without taking into consideration the resistance caused by friction and drag(as these will be equal on both vehicles at the 100kmh mark and negate each other) The positive force applied on car 1 when shut off would be F=1600x0

F=0

The coefficients of drag and friction would slow the vehicle from 100

Car 2

Accelerating from standstill to 100 (because it is a Expensive Daewoo we will say 8 second) therefore

F = ?

m = 1600

a = v-u/t

Therefore

v=100

u= 0

t = 8

100-0/8 = 12.5

a= 12.5 m/s squared

1600 x 12.5 m/s squared

Therefore

Vehicle 2 hitting 100 still has 20000N or 20 kn still being applied as it hits 100.. The curve would be parabolic but as the force decreased back to zero the speed would creep above 100.

Contrary to this is the laws of momentum that state

Momentum = p

p= mv

m= 1600

v = 21 m/s

p = 33600 kg m/s

Therefore both vehicles have the same momentum at 100 kmh therefore stopping at the same distance from shutdown.

The formula for Conservation of Momentum

Ptot =P'tot m1V1 + m2V2 + m3V3 = m1V'1 + m2V'2 + m3V'3

[Honest Gaza]

Yeh, but what is the answer

[rushed6]

depends on who done the edit and if brake shudder is an issue

[Blonk]

Vehicle 2 gaza.........

[harvyk]

Can anyone else see where this is going, - fordxr6turbo.com flight number #125 is still delayed on the giant treadmill on the runway because of a thread like this...

[DBOSS]

  rushed6 said:

depends on who done the edit and if brake shudder is an issue

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