Answer 2:
Well, it's quite hard to have a car go at the
speed of light, impossible according to the
special theory of relativity. (I'm not going to
get into the general theory of relativity because
that's a more confusing issue.)
Here's the easy way to understand why: remember
the famous equation E = m c ^{2} ?
E is the energy of the car, m is the
mass of the car, and c is the speed of
light. Really this equation isn't quite
explanatory enough.
Let's say the mass m is the mass of the car
when it is at rest, or "rest mass" . Then
the equation is really
E = m c ^{2}/(1 
v^{2}/c^{2})^{(1/2)}
(note that c and v are to the 2nd power, so
the power(1/2) is the square root of the stuff in
parentheses). Here v is the speed of the
car. So you can see that when v gets close to
c, the denominator gets close to zero, which means
that the energy gets very, very big. In
fact, the energy is infinite if you try to go at
the speed of light.
On the other hand, if your car went very close
to the speed of light past me, I would see the
light coming out of your headlights at the speed
of light. You, sitting in your car, would also see
the light come out at the speed of light. This is
what relativity tells us!
