Find for how much time, the car with stop and how many meter

[MaiteB]

Homework Statement

A car with mass 1000kg moves with velocity 50 km/hour. The system of deceleration in a car is based on the principle of "force match" that is applied on each of four wheels with a force of 210 N and the ray of the wheel is 0.3m. Find for how much time, the car with stop and how many meters it has done. I thought this: a=F/m=0.21, a=v/t=> t=66,14 S but in my book solution it is 4.96 S.

Homework Equations

a=F/m, a=v/t

The Attempt at a Solution

I thought this: a=F/m=0.21, a=v/t=> t=66,14 S but in my book solution it is 4.96 S

 

[BvU]

Hello Maite,

That is a very interesting deceleration principle, but I have never heard of it and can't even find a hint of it anywhere.

But in your working, I see you only use one wheel to brake. Using four wheels would already reduce the braking time to 16.53 s.

And then the ratio of the book answer to your result is exactly 0.3.

Could it be that the braking system exerts a torque of 210 Nm on each of the wheels, which -- with a wheel radius of 0.3 m -- translates into a braking force of 700 N for each of them, so 2800 N in total ?