Question

What is the magnitude of the net force needed to bring a 2110 kg car to rest from 18.1 m/s in 7.0 seconds?

Answer 1

Here is what we know:
a = ?, s = ?, u = 18.1m/s, v = zero/rest, t = 7.0s, m = 2110kg

(a = acceleration, s= displacement, u = initial velocity, v = final velocity, t = time and m is mass)

Now we choose a kinematic formula. Since we know v, u and t, we will use the formula: v = u+at and rearrange it so that we can find a.
a = v-u/t
a = 0-18.1/7.0 = -2.5857...
therefore, a = -2.6m/s

We have our acceleration, now let’s find the net force. To find the force we use one of Newtons laws of motion.
We will use Newtons second law since it describes what happens when one or more forces act upon an object.
F = ma
F = (2110kg)(-2.6m/s)
F = -5486 kg
Therefore the net force F = -5486 N