1-D Kinematics Example: The case of the falling grapefruit

Kinematics problems involve an object (or objects) in motion and these generally come in the form of word problems. Let’s go through an example together. The word problem we will be looking at is written below.

Word problem: Longtime friends, Maureen and Roger, are having a picnic on the rooftop of their apartment building. A grapefruit gets accidentally dropped from the rooftop and falls straight down to the ground. The falling grapefruit falls past their neighbor Paloma’s window. The grapefruit takes 0.125 s to fall from the top to the bottom of Paloma’s window, a distance of 1.20 m. From the bottom of the window it takes 1.0 s for the grapefruit to hit the ground. How tall is the apartment building?

Reading and setting up the problem

Watch the video below to see a walkthrough of reading the problem and determining the following:

• The goal (or what variable we are being asked to solve for)

• The variables/information given

• How to diagram the information

• Determining potentially useful equations

Now that you’ve setup the problem, see if you can come with a problem solving strategy to determine Δx, the height of the apartment building. Once you’ve thought about your possible strategy, check out the two videos below for a couple of strategies that we came up with.

Note that everyone has different problem solving experiences, so our thought processes and thus problem solving strategies might be different. For this particular problem (and for many problems) several valid problem solving strategies exist.

Strategy 1

Strategy 2