How do I remember which formulas to use when studying 1-D Kinematics?

Generally used kinematic equations :

• #s_f=s_i+v_(is)Deltat+1/2a_s(Deltat)^2#

• #v_(fs)=v_(is)+a_sDeltat#

• #v_(fs)^2=v_(is)^2+2a_sDeltas#

Where:

• #s_f# is the final position
• #s_i# is the initial position
• #Deltat# is the time interval over which the motion occurred, where #Deltat=t_f-t_i#
• #Deltas# is the change in position over the motion, where #Deltas=s_f-s_i#
• #v_i# is the initial velocity
• #v_f# is the final velocity
• #a_s# is the acceleration of the object in the direction of the position you are measuring (i.e. #a_y# if you are looking at an object moving vertically or #a_x# if you are looking at an object moving horizontally)

Here it seems the preference of your teacher is to use #v_0# for initial velocity and #v# for the "final" or current velocity. We would then have:

• #s=s_0+v_(0s)Deltat+1/2a_s(Deltat)^2#

• #v_s=v_(0s)+a_sDeltat#

• #v_s^2=v_(0s)^2+2a_sDeltas#

So, for you:

• #x_0# is the initial #x# position
• #V_x# is the final or current horizontal or #x# velocity
• #V_(x0)# is the initial horizontal velocity
• #A_x# is the horizontal acceleration

Which equation you use will depend on which variable you are trying to solve for.

For example:

• If you're looking for the change in position but don't have time, you would use the third equation
• If you're looking for change in position and you do have time, but you don't know anything about the final velocity, you would use the first equation

etc.

You fill in for each factor/variable the value and the units. One variable will be missing and one not mentioned at all in the data. Put a question mark beneath the factor you are told to find and a horizontal dash under the irrelevant one.

Each of the kinematic equations is missing one of the variables, look through them carefully and you'll see what I mean. This is how to decide which equation to use when you are starting out, with enough practice it does become obvious (promise!)