Aim How do we use the kinematics formulas

Aim: How do we use the kinematics formulas? Quiz Tomorrow Do Now: What is the difference between average velocity and instantaneous velocity?

On the back of your reference table • You can find the two formulas we have been using so far to find the average velocity or speed and average acceleration. • You can also find the 3 new kinematics formulas.

New Kinematics formulas • vf= vi + at • d=vit+ ½ 2 at • vf 2= vi 2+ 2 ad • • • vf= final velocity vi = initial velocity a= acceleration t= time d= distance

Initial vs. Final velocity • Initial velocity is the starting velocity of an object. • Final velocity is the velocity reached at a later point in time.

Acceleration • The change of the object’s velocity over time. • Recall that acceleration is the final velocity – the initial velocity / time.

Example • A car accelerated from rest to 25 m/s. • • What are the initial velocity? Final velocity? Acceleration? If it traveled for 15 s what distance did it cover?

Example Answers • Initial velocity: car stated from rest. Vi = 0 m/s • Final velocity: The problem states to 25 m/s Vf • Acceleration = (25 m/s – 0 m/s )/ 15 s = 1. 666666 m/s 2= 1. 7 m/s 2

Solving for distance by GUESS method • Given: vi = 0 m/s, vf = 25 m/s t= 15 s a= 1. 7 m/s 2 • Unknown: distance = ? ? ? • Equation : d=vit+ ½ at 2 • Substitute: d= (0 m/s)(15 s)+ ½ (1. 7 m/s 2) (15 s)2 • Solve: d= ½ (1. 7 m/s 2) 225 s 2= 191. 25 m = 190 m