Answer:
40 m
Explanation:
A car travelling at 45 ms has a kinetic energy of
Ec = 1/2 * m * v^2
We do not know the mass, so we can use specific kinetic energy:
ec = 1/2 * v^2
In this case
ec = 1/2 * 45^2 = 1012 J/kg
If it stops in 10 m, the braking force performed a sppecific work of 1012 J/kg in 10 m
L = F * d
F = L / d
F = 1012 / 10 = 101.2 N/kg
If the car is running at 90 m/s, the specific kinetic energy of:
ec2 = 1/2 * 90^2 = 4050 J/kg
With the same braking force the braking distance is:
d2 = L2 / F
d2 = 4050 / 101.2 = 40 m
