Unit 2 Class Notes

Accelerated Physics

The Kinematics Equations (1D Equations of Motion)

Day 8

Review for test

Step #1

Write Down What You Have (Look for “Key” Words)

“Coming to a stop”

“Starting from rest”

“Coasting”

“Maximum Height”

“Dropped”

v2 = 0

v1 = 0

v1 = v2 = constant

v2 = 0

a = -9.8 m/s2

“Slowing Down”

“Braking”

“Speeding up”

“Accelerating from rest”

a = - __

a = + __

Step #3

Solve the Equation

Step #4

Make sure your answer makes sense

Some Helpful Tips From the Master

Helpful Tip #1

Choose your “Key Points” in every

problem…and do so wisely.

“Free-fall”

“Throw up”

v1 = 0

v2 = 0 (at top)

Vertical Problems

1

2

2

1

v1 0

1

2

“Throw-downs”

“Throw up / Come Down” (throw and catch at same height)

v2 = 0 (at top)

Vertical Problems

2

1 3

t12=t23

v1 =-v3

“Throw up / Come Down” (throw and catch at different heights)

Use and solve quadratically for “t”

x13 =

2

1

3

2

1

3

x13 =

x 12 ( 9.8)t

2 v1t

Helpful Tip #2

Assign positive and negative to different

directions.

Helpful Tip #3

When solving a quadratic equation, do so with minimal

effort.

Solving a quadratic equation

Choice A Choice B

b b2 4ac2a

Factoring

Choice C

2nd Trace Zero (on graphing calculator)

Unlikely on a physics problem

Helpful Tip #4

Get out of the habit of trying to use “Chris

Farley” when “Leonardo” is

necessary.

d = rt(Can be used only at

constant speed)

x 12 at

2 v1t

Can be used at constant speeds (a=0) or when

accelerating. Awesome Dude!

Helpful Tip #5

When dealing with a chase problem, use

“New-Look” Leo (built for the chase)

Chase Problems

x2A x2B12 atA

2 v1A tA x1A 12 atB

2 v1B tB x1B

Since the two objects (A and B) end up at the same position by the end of the chase, use …

But what if…

x2A x2B12 atA

2 v1A tA x1A 12 atB

2 v1B tB x1B

The objects start at different places?

It’s already accounted for here and here

But what if…

x2A x2B12 atA

2 v1A tA x1A 12 atB

2 v1B tB x1B

The objects start at different TIMES?

You’ll need to use an extra equation relating the two times. Plug this new

equation into the long equation above.

Example: tA = tB + 1

Helpful Tip #6

It is always important to remember that when

something is thrown up or down (or simply falls), the acceleration at ALL times is

constant.

The acceleration of the ball at EVERY point on this red path (When it’s rising up, when it’s stopped, when it’s falling down) is always -9.8 m/s2.

+

-

An object thrown up has a constant acceleration at ALL times….

….the acceleration due to gravity

Objects rise and fall in the same amount of time

(assuming no parachute )

t

x

t

v

Constant slope = constant accel.

Your training is complete. Now go, have some hot tea, and rest for the upcoming

Unit 2 Test

TONIGHTS HWComplete Review Worksheet