does a car work faster if it's heavy or if it's light?

Simplified answer.

If you made a car heavier, you have (basically) two choices:

1) Make the car work the same amount, in which case it will move slower.

2) Make the car work harder to match it's previous speed.

This is over-simplification as you can gow faster than before if you make it work hard enough.

Hope this helps!

Put a 100 lb bag of books on your back and see if you go faster.

Think about it. The heavier the car is the more work the engine needs to do to move it and the harder it is on the brakes, tires, etc. Any and all unnecessary weight is stripped from a race car.

Alison aka Nice Lady, you just said it works harder, but does it work faster? Or does it work harder but slower? I don't understand that myself.

lets consider the body to be of mass---m1

and acceleration---a

therefore force acting on the car would be

F1=m1.a

work done therefore would be

W1=F1.a=m1.a.a

now consider a lighter body of mass---m2=m1-x (where "x" is the difference in masses)

and acceleration a

here force acting on the body would be

F2=m2.a=(m1-x)a

here work done is

W2=F2.a=(m1-x).a.a

fom this we can observe that

"W1"is greater than "W2"

that is work done by the same motor in for moving a heavier car,is greater than the work done in moving a lighter car provided that the acceleration remains constant