Help with a homework question?

You are absolutely right, and your method using 'work and energy' is perfect.

However, you can also solve this problem using 'simple kinematics' ...

Let me show you ;-)

I *could* first convert km/h to m/s, but in this case it isn't really necessary.

To keep all the units consistent, I'll convert the 10 m to 0.01 km instead.

Find the deceleration of the car driving at 30 km/h, using

v² = u² + 2×a×s

(0 km/h)² = (30 km/h)² + 2×a×(0.01 km)

-900 km²/h² = a×(0.02 km)

a = -45000 km/h²

(Note the units for acceleration. They are 'strange', but technically correct)

Now apply that acceleration on the car driving at 60 km/h.

(0 km/h)² = (60 km/h)² + 2×(-45000 km/h²)×s

-3600 km²/h² = (-90000 km/h²)×s

s = 0.04 km

s = 40 m

See how, in the end, all the units fall straight in their places ??? ;-)

Ok so if it s going 30 km/h is 10 meters and u are now doing 60 km/h and doing every thing the same you would just multiply by 2 because 30 x 2 = 60 so 10 x 2 = 20 so your answer would be 20

30 = 10

60 = ??

30*a = 60*10 =

30a = 600 you must make the A 1 so you have to get rid of the 30

30a / 30 = 600 / 30

A = 20

20m