Explanation:

Calculating Final Velocity

An airplane lands with an initial velocity of 70.0 m/s and then accelerates opposite to the motion at 1.50 m/s2 for 40.0 s. What is its final velocity?

Strategy

First, we identify the knowns: v0=70m/s,a=−1.50m/s2,t=40sv0=70m/s,a=−1.50m/s2,t=40s.

Second, we identify the unknown; in this case, it is final velocity vfvf.

Last, we determine which equation to use. To do this we figure out which kinematic equation gives the unknown in terms of the knowns. We calculate the final velocity using Equation 3.12, v=v0+atv=v0+at.

Solution

Substitute the known values and solve:

v=v0+at=70.0m/s+(−1.50m/s2)(40.0 s)=10.0 m/s.v=v0+at=70.0m/s+(−1.50m/s2)(40.0 s)=10.0 m/s.

Figure 3.19 is a sketch that shows the acceleration and velocity vectors.