Question

Calculate the force (in n) needed to bring a 950 kg car to rest from a speed of 95.0 km/h in a distance of 125 m (a fairly typical distance for a non-panic stop).

Answer 1

Let's convert the final speed of the car into m/s:

`v=95 km/h = 26.4 m/s`

We can find the acceleration of the car by using:

`2aS= v_f^2-v_i^2`
where vi=0 is the initial speed of the car, vf=26.4 m/s the final speed, a the acceleration and S=125 m is the distance covered.
By substituting numbers and re-arranging the formula, we find:

`a= (v_f^2-v_i^2)/(2S)= ((26.4 m/s)^2)/(2\cdot 125 m)=2.79 m/s^2`

And then, we find the force by using Newton's second law:

`F=ma=(950 kg)(2.79 m/s^2)=2651 N`