(a) calculate the force needed to bring a 950-kg car to rest from a speed of 90.0 km/h in a distance of 120 m (a fairly typical distance for a non-panic stop). (b) suppose instead the car hits a concrete abutment at full speed and is brought to a stop in 2.00 m. calculate the force exerted on the car and compare it with the force found in part

(a)

mass of the car: m=950 kg

Initial speed:

Final speed: (the car comes to rest)

distance:

We can find the acceleration by using the following SUVAT equation:

Re-arranging it and replacing the numbers, we find the acceleration

So now we can calculate the force using Newton's second law:

And the negative sign means the force is applied against the direction of motion.

(b)

In this case, the distance is different:

so, the acceleration in this case is

And so, the force applied in this case is

which is much larger than the force exerted in the previous exercise.