provides. The problem states that acceleration is constant, so that means we can use our kinematics
equations. Also, it asks us to find two values, a time and a distance. Based on the information in the
problem, we know that the time needed for the car to reach 120 m/s is greater than 6 s because it took 6 s
for the car just to reach 60 m/s. Moreover, we can estimate that the car will travel several hundred meters
in total, because the car’s average velocity must be less than 120 m/s, and it travels for several seconds.
So now let’s solve the problem. We’ll use our four-step method.
Step 1 : Table of variables.
The car begins at rest, so v 0 = 0 m/s. The final velocity of the car is 120 m/s. We’re solving for time and
displacement, so those two variables are unknown. And, at least for right now, we don’t know what the
acceleration is.
Step 2 : Count variables.
We only have two values in our chart, but we need three values in order to use our kinematics equations.
Fortunately, there’s enough information in the problem for us to solve for the car’s acceleration.
Acceleration is defined as a change in velocity divided by the time interval during which that change
occurred. The problem states that in the first 6 s, the velocity went from 0 m/s to 60 m/s.
We now have values for three of our variables, so we can move to Step 3 .
Step 3 : Use “star equations” to solve.
All three of our known values can be plugged into *, which will allow us to solve for t .