# Tue Sep 10

Mechanics

Nov 14, 2013 (4 years and 8 months ago)

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Tue Sep
10

Attendance

Announcements

Homework

Warm
-
up

1 D kinematics 1 & 2

Homework

WS 1 D Kinematics 1 & 2

Study for quiz

Warm
-
up

You know your car can accelerate from 0 to
60 m/s
in
5.2 s.

What is the acceleration?

If you could keep doing this for 1 hour,
what would your
final
speed be?

What have we studied so far?

GP
1

Converting Units

Scientific Notation

SOHCAHTOA

Vectors

Speed

Velocity

Acceleration

1D Kinematics

Go through the different labels we have

x
i
,

x
f
,

v
i
,

v
f
,

a

t

Start teaching it with 1
column

X

x
i
,

x
f
,

v
i
,

v
f
,

a

t

What are our two formulas right now?

Then how would you find the final distance
if you know
the
initial speed, acceleration,
and time.

x
f

=

You are in a plane, you know that the plane
can accelerate
at
a rate of 10 m/s
2

and you
are starting with an initial speed of 5 m/s
and x = 0 m.

How far have you traveled after

1 s

10 s

You are base jumping you are told to wait 5
s before
pulling

Gravity is 9.81 m/s
2
speed and
distance
0.

What is your final speed and how far have
you dropped at
this
point?

What are our current formulas for kinematics
and what
are
they missing?

Another formula for kinematics if you don't
have time

v
f
2

=

If you are not given x
i

or v
i

then most times
it's going to be 0. Use that to help simplify
the problem.

You are driving a car, traveling with a velocity
of
25
m/s, when you see a child suddenly run
into the
street
. The car slows with a steady
acceleration of
-
8.5 m/s
2

and comes to a
stop.

How far did you go before you stopped?

How long does it take you to stop?

More examples of 1
-
D kinematics

What are the equations that we have for
kinematics?

What do you need to solve for first?

You want to get onto the freeway. You only
have 200 m
to
reach a speed of 28 m/s

What does your acceleration need to be to
reach the
needed
speed?

How
much time is needed?

A car is traveling with a speed of 30 m/s. It
needs to
stop
. The car can only slow down at
a rate of 2 m/s
2
.

How
long will it take for the car to stop?

How
far would the car need to travel before it
can stop?

A 9 mm bullet leaves the barrel at the
speed of 200 m/s.

If the barrel is only 10 cm long, what is the
acceleration
of
the bullet?

How long does it take the bullet to leave
the barrel?

A sniper rifle has a barrel length of 0.75 cm.

The bullet leaves the barrel with a speed of
400 m/s.

What is the acceleration of the bullet and
how long does
it
take the bullet to leave
the barrel?

To land on the aircraft carrier, the plane
must slow down
from
72 m/s to 0 in 2
seconds. What is the acceleration?

How
much room does the plane need?