If a car goes the speed of light and turns its headlights on what happens?

Since it takes infinite energy to accelerate to light speed, there is nothing left to power the lights. Don't try it, you'll burn out your alternator and you'll be a loooong way from the nearest service station.

Depends on who's asking.

If you're the driver, then nothing happens. Your relative velocity within the car is v = 0; so the Lorentz transformation is L(v = 0) = sqrt(1 - (v/c)^2) = sqrt(1) = 1 and there is no observable change in length, time, and mass. This is, in fact, why Einstein's theory is called the Theory of Relativity, what we see is relative to the framework we see it from.

On the other hand, if you're the traffic cop watching this crazy driver whiz by in his souped up Enterprise class car driven by singularity energy, plenty might happen...depends on where the cop is when sighting (maybe) the car.

At v = c, light speed, the cop would see the car totally disappear when looking in the direction of the car from its side. That results because l = L L(c) = 0; where L is the rest length of the car and L(c) = sqrt(1 - (c/c)^2) = 0 is the Lorentz Transform at light speed. In fact, the cop would never see the car because, at light speed, it would have shrunk to nothing in length (the direction of travel). And the light beams would have shrunk to nothing as well since they, too, are traveling at the speed of light.

End on (either taillights or headlights), the cop would see no change in dimensions; so the car and lights would appear normal. But, and this is a big BUT, the car and its lights would be traveling at or away from the cop at the speed of light. And, given that the mass of that car appears infinite from m = M/L(c) = M/0 ---> infinity, that cop better get out of the way if he's in front of the car.

To make matters worse, light reflecting off the car and the car would be traveling at the same velocity; so the cop would not see the car until is was upon him since light from the car and the car would reach the cop at the same time. (This is why I wrote "maybe" earlier.)

Finally, the cop would need to wait a very very long time to give out the speeding ticket. That results from t = T L(c) = L*0 = 0; where T is the rest time the cop is experiencing and t is the time passage the cop sees on board the car. In other words, the cop sees no time passing in the car even though billions of years (actually an infinite time lapse) pass for the cop. This long waiting period exists even at slightly less than light speed. Thus, the driver, thinking time is passing normally, would turn around and come back to Earth only to find it no longer existed and that cop had long since passed away without ever giving out that speeding ticket.

Of course this is all fantasy based on the impossible speed of light premise. But the effects are real; so even at, say, v = .1c, 1/10 light speed, they show up. And perhaps, some day, mankind will be able to travel at or about 30,000 km/sec (1/10 light speed). In which case L(.1c) = sqrt(1 - (.1)^2) = sqrt(.99) ~ .99 so that t = .99 T, m = M/.99, and l = .99 L and the relativity effects on that space car will be observable.

First of all, no object can obtain the speed of light except EM.
Second, Chelseablue is correct if that's what happen.
Third, 1000mph+1000mph is NOT 2000mph because the missile have only the energy to propel itself to 1000mph related to us.

CHECK YOUR GENERAL THEORY OF RELATIVITY.

That's the question Einstein asked.
If you traveled at the speed of light you would travel from point to point instantaneously, in your time.You wouldn't have time to turn on the lights.
The distance from point to point would also be zero from your point of view. ( The spacetime interval from event to event would be zero for everyone.)

go to my website http://www.geocities.com/spacetimeexercises/

First of all, no object can obtain the speed of light except EM.
Second, Chelseablue is correct if that's what happen.

You never see the headlights come on before it hits you, and time stands still for the car

You can't turn on the headlight because you need infinity energy to turn.

i dnt thnk it wl mek mch of a difference to d lght of d headlight. they'l keep travellng, 1st d lght of d headlght, then the car behnd it. the car wll possbly exceed escape vel., so it wl go out of earth in2 d space.

Think of a jet fighter going 1,000 MPH and think of a fired bullet travelling 1,000 MPH.

If that jet fighter is flying and fires that bullet from one of its guns, then that bullet is effectively travelling at 2,000 MPH. (Because even unfired, it was already travelling at 1,000 MPH just by riding in the jet.)

Same thing with your example of the car moving at the speed of light and the headlight turning on while it's moving.

The beam from those headlights would move at twice the speed of light.