Dynamics Example

Dynamics problems are problems where we figure out how an object will move and then it becomes a kinetic problem. We will look at the forces acting upon an object (or objects) and determine the motion. The word problem we will be looking at is written below.

Word problem: Your physics class is getting new textbooks, and your professor asks you to walk to the bookstore and bring the class set to the science building. So, you must drag a crate of books across the floor by pulling on a rope tied to the crate. You exert a force of magnitude F = 450 N on the rope, which is inclined at an angle Θ = 38° to the horizontal, and the floor exerts a horizontal force of magnitude f = 125 N that opposes the motion. Calculate the magnitude of the acceleration of the crate if (a) its mass is 310 kg and (b) its weight is 310 N. 

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

Now that you’ve set up the problem, see if you can come with a problem solving strategy to determine the acceleration of the crate, a. Once you’ve thought about your possible strategy, check out the video below to check your answer (remember there is usually more than one way to solve for the correct answer).

Option for solving: