Let

1
Lets practice using the kinematics equations

• One more equation
• vf2 vi2 2a?d

2
Kinematics Equations

• vf v i a ?t
• ?d 1/2 (vi vf) ?t
• ?d vi ?t 1/2 a ?t2
• vf2 vi2 2a?d

3
Problem

• A soccer player, running at a speed of 2.6 m/s,
  decides to accelerate. For the next 18 m, he
  speeds up with an acceleration of 0.45 m/s/s.
  What is his speed at the end of the run?

4
Problem

• The length of the barrel of a primitive blowgun
  is 1.6 m. Upon leaving the barrel, a dart has a
  speed of 24 m/s. Assuming the dart is uniformly
  accelerated, how long does it take for the dart
  to travel the length of the barrel?

5
Gravitational Acceleration
6
Which vector represents the skiers acceleration
at the instant shown?
A
B
C
D
7
Which vector represents the skiers acceleration
at the instant shown?
A
B
C
D
8
When do we use g?

• When does something have an acceleration of 9.8
  m/s/s down?

9
When do we use g?

• When does something have an acceleration of 9.8
  m/s/s down?
• Always use the operational definition.

?v
a

?t
10
When do we use g?

• When does something have an acceleration of 9.8
  m/s/s down?
• Always use the operational definition.
• Everything has an acceleration g

?v
a

?t
11
When do we use g?

• When does something have an acceleration of 9.8
  m/s/s down?
• Always use the operational definition.
• Everything has an acceleration g IF it is
  falling off the physics building in a vacuum.

?v
a

?t
12
Which falls faster, a big rock or a small rock?
13
The ball and the feather
14
A short thought experiment
15
A short thought experiment
16
A short thought experiment
GLUE
17
Cliff Diving
18
Cliff Diving
19
Problem

• You and a friend stand on the edge of a 40 m
  cliff. You throw a red ball straight up at 30
  m/s. At the same time, your friend throws a blue
  ball straight down at the same speed.
• Compare the velocities of the two balls right
  before they hit the ground.
• How much later does the red ball hit than the
  blue ball?

20
0 m/s
10 m/s
20 m/s
30 m/s
21
0 m/s
3 sec
22
0 m/s
3 sec
30 m/s