How to

Solve

Physics

Problems

7 Step Guide to Problem

Solving

Step #1

Put your calculator down!

Step #2

Read the problem thoroughly.

Key into words like: constant, from rest,

accelerating, coming to a stop

7 Step Guide to Problem

Solving Step #3

A. Identify

Known Variables, fill in the chart

Variable Value

Vi (Initial Velocity)

Vf (Final Velocity)

a (acceleration)

∆X (Change in Distance)

∆t (time interval)

∆D

7 Step Guide to Problem

Solving

B. Determine what you are solving for?

o Variable that you are being asked to find.

C. Draw a sketch of the scenario.

f iV V a t

21

2ix V t a t

2 2 2f iV V a x

1( )

2f ix V V t

!

! !fiavg

x nv v v

t r n r

Step #4: Pick an Equation

7 Step Guide to Problem Solving

o Step #5: Rearrange the equation to solve

for desired variable

EX: We selected this equation:

Rearrange to solve for a.

7 Step Guide to Problem Solving

f iV V a t

f iV V a t f iV Va

t

7 Step Guide to Problem

Solving

o Step #6: Solve

o Start plugging in values for known variables.

o Step #7: Check your answer

o 1. Does the answer make sense?

o 2. Are the units correct?

Example Problems

A car starts from rest and accelerates to a

velocity of 25 m/s over a distance of 100

meters. How long did it take the car to

reach 25 m/s?

Step #2: Key terms

Example Problems A car starts from rest and accelerates to a

velocity of 25 m/s over a distance of 100

meters. How long did it take the car to

reach 25 m/s?

Step #3: Table

Solving for t

Variable Value

Vi

Vf

a

∆X

∆t

0

25 m/s

?

100 m

?

Example Problems A car starts from rest and accelerates to a

velocity of 25 m/s over a distance of 100

meters. How long did it take the car to

reach 25 m/s?

Step #4: Select equation

Variable Value

Vi 0

Vf 25 m/s

a ?

∆X 100 m

∆t ?

1( )

2f ix V V t

Example Problems A car starts from rest and accelerates to a

velocity of 25 m/s over a distance of 100

meters. How long did it take the car to

reach 25 m/s?

Step #5: Rearrange Equation

1( )

2f ix V V t

2

( )f i

xt

V V

Example Problems A car starts from rest and accelerates to a

velocity of 25 m/s over a distance of 100

meters. How long did it take the car to

reach 25 m/s?

Step #6: Solve

2

( )f i

xt

V V

2(100 )8.0

(25 / 0)

mt s

m s

Example Problems A car starts from rest and accelerates to a

velocity of 25 m/s over a distance of 100

meters. How long did it take the car to

reach 25 m/s?

Step #7: Check

1. Is the answer reasonable?

2. Are the units correct?

Example Problems

A ball is thrown straight up in the air with an

initial velocity of 10 m/s and then caught at

the same height 2 seconds later.

a) What is the acceleration of the ball after

it leaves the throwers hand?

b) How high will the ball go up before

falling back down?

Example Problems

A ball is thrown straight up in the air with

an initial velocity of 10 m/s and then

caught at the same height 2 seconds

later.

Step #2: Key Terms

Step #3: Table

Variable Value

Vi

Vf

a

∆X

∆t

0 m/s

10 m/s

?

?

1.0 s WHAT? Why 1.0 sec?

Example Problems A ball is thrown straight up in the air with

an initial velocity of 10 m/s and then

caught at the same height 2 seconds

later.

a) What is the acceleration of the ball after

it leaves the throwers hand?

Step #4: Select an Equation

Step #5: No need

to rearrange 21

2ix V t a t

Example Problems

Step #6: Solve

a) What is the acceleration of the ball after it leaves the

throwers hand?

Variable Value

Vi 0 m/s

Vf 10 m/s

a

∆X ?

∆t 1.0 s

9.8 m/s2

For problems that

occur in the air,

the acceleration is

due to gravity and

is always 9.81 m/s

Example Problems

21

2ix V t a t

2 21(0)(1.0 ) (9.8 / )(1.0 )

2x s m s s

b) How high will the ball go up before

falling back down?

Ans: 4.9 m