# Homework Help: Question about choosing which Physics equation to use?

1. Jan 17, 2014

### JessicaJ283782

So, when you are trying to solve a problem (we are currently learning about velocity, acceleration, time, distance, Kinetic Motion equations), how should you approach the problem?

I've heard list the variables you know, and then figure out which variables you have, which will determine which equation you use.

However, I get confused when making sure I have all of the variables. For example, how do you tell if there is a final velocity if they don't specifically say it? If they have an "initial velocity" listed, is there always going to be a final velocity hidden somewhere in the problem?

2. Jan 17, 2014

### Simon Bridge

There are two main approaches to kinetic problems given in secondary school.

1. memorization:
What you said. There should be one equation (out of five) that has one unknown.

2. use velocity-time graphs
Sketch the v-t graph for the motion ... you will have to put letters in for some of the values.
recall that the slope of the graph is the acceleration and the area under it is the displacement - write this out, using the graph to guide you. (this way you don't need to memorize any kinematic equations.)
now you have two equations with two unknowns: simultaneous equations.

Most people seem to use method 1, but only remember about 3 equations so they have to use two of them and some algebra.