x =
v
o
t + ½at
2
x = ½at
2
2
x/a = t
2
t
2
= 2
x/a
/
2
t
x
a

77
1. A ball is dropped from a very tall building.
Find the ball’s position and velocity after 2 seconds.

78
White board problems
WB13) A book falls off .75 meter tall desk.
a)
How long does it take to reach the ground?
What Equation do we need?

79
A ball is thrown straight up in the air, find the
acceleration and velocity at various points in its
path.
Gravity always causes an
acceleration
downward
.
v = 19.6 m/s, up
a = 9.8 m/s
2
, down
v = 19.6 m/s, down
a = 9.8 m/s
2
, down
v = 9.8 m/s, down
a = 9.8 m/s
2
, down
v = 0 m/s
a = 9.8 m/s
2
, down
v = 9.8 m/s, up
a = 9.8 m/s
2
, down

80
Ex 11) A rock is dropped from rest from a tall
building.
How far has it traveled after 3
seconds?
0 m/s
___
9.8 m/s
2
3 sec
x =
v
o
=
v
f
=
a
=
t
=
? m

81
Ex 12) A ball thrown down from a 20 m tall
building with a speed of 15 m/s.
How fast is it
moving when it hits the ground? (choosing up as
positive)
x =
v
o
=
v
f
=
a
=
t
=
-20 m
-15 m/s
?
-9.8 m/s
2
?

82
Ex13) A ball thrown upwards from a 20 m tall
building with a speed of 15 m/s.
How fast is it
moving when it hits the ground?
x =
v
o
=
v
f
=
a
=
t
=
-20 m
15 m/s
?
-10 m/s
2
?

83
WB14) A ball is thrown with a velocity of 25 m/s
straight up.
(a)How much time does it take to reach
the top
of its path?
x =
v
o
=
v
f
=
a =
t =
?
25 m/s
0 m/s
at top
- 10 m/s
2
?
v = v
o
+ a
t
v - v
o
= a
t
0 m/s – 25 m/s
- 10 m/s
2
t
=
t
=
2.5 s
v
f
- v
o
a
t
=
Solve the following problem completely:

84
(b) How high does
the ball go?
x =
v
o
=
v
f
=
a =
t =
?
25 m/s
0 m/s at top
- 10 m/s
2
2.5 s
x
= v
o
t + ½at
2
x
= (25 m/s)(2.5 s) + ½(-10 m/s
2
)(2.5 s)
2
x
= (62.5 m) + (- 31.25 m)
x
= 31.25 m

85
White board problems
WB15) A ball is dropped from a 45 meter tall
building.
a) How long does it take to reach the ground?
b) how fast is it moving after 2 seconds?
c) How fast is it moving when it hits the ground?

86
White board problems
WB15) A ball is dropped from a 45 meter tall
building.
a) How long does it take to reach the ground?
b) how fast is it moving after 2 seconds?
c) How fast is it moving when it hits the ground?
15)
a)
3 seconds
b)
20 m/s
c)
30 m/s

87
WB14) Hubble throws a bone straight up with a
speed of 35 m/s
a) For how much time is it in the air?
b) What is its velocity after 3.5 seconds?
c) What is its velocity after 4 seconds?
d) What is its velocity after 5.3 seconds?
e) How high does the bone go?

88
WB14) Hubble throws a ball straight up with a
speed of 35 m/s
a) For how much time is it in the air?
b) What is its velocity after 3.5 seconds?
c) What is its velocity after 4 seconds?
d) What is its velocity after 5.3 seconds?
e) How high does the banana go?
14)
a)
7 seconds b)
0 m/s (at top)
c)
-5 m/s d)
-18 m/s
e)
61.25 m

89
WB15) A man stands on top of a tall building and
throws a rock straight down at 15 m/s.
It takes 4.5
seconds to hit the ground.
a.
How tall is the building?
b. How fast is the rock traveling right
before
it hits the ground.

90
WB15) A man stands on top of a tall building and
throws a rock straight down at 15 m/s.
It takes 4.5
seconds to hit the ground.

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- COOKE
- Acceleration, Velocity, m/s