Transcript Class 8, 28 June

SMDEP Physics
Newton’s Laws
Ch 4, #35(a): forces on stationary
buckets (top, bottom)
34 N, 68 N
68 N, 68 N
68 N, 34 N
68 N, 68 N
Other
Didn’t finish
91%
2%
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fin
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0%
th
e
N
8
N,
6
68
68
N,
3
4
N
0%
N
8
N,
6
68
N,
6
8
N
2%
O
4%
34
1.
2.
3.
4.
5.
6.
Ch 4, #35(b): forces on accelerating
buckets (top, bottom)
40 N, 80 N
80 N, 40 N
34 N, 68 N
80 N, 80 N
Other
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2%
id
n
’t
fin
r
is
h
0%
th
e
N,
8
0
N
0%
N
80
34
N,
6
8
N
0
N,
4
80
N,
8
0
N
0%
O
2%
40
1.
2.
3.
4.
5.
6.
96%
Ch 4, #36a: force by window washer
284 N
568 N
142 N
1116 N
Other
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91%
is
h
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th
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N
16
11
2%
0%
r
0%
N
14
2
N
8
56
4
N
2%
O
4%
28
1.
2.
3.
4.
5.
6.
Ch 4, #36b: acceleration of window
washer
0.5 m/s2
1.0 m/s2
2.0 m/s2
Other
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38%
9%
7%
is
h
id
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th
e
O
2
0
2.
m
/s
2
0
1.
m
/s
5
m
/s
2
2%
0.
1.
2.
3.
4.
5.
44%
Ch 4, #41: How far up plane? How much
time?
4.4 m, 4.4 s
8.8 m, 8.8 s
2.2 m, 2.2 s
Other
Didn’t finish
9%
is
h
’t
fin
id
n
O
th
e
r
s
.2
2
2.
m
,2
.8
8
8.
m
,8
.4
4
m
,4
2%
s
2%
s
2%
4.
1.
2.
3.
4.
5.
85%
Ch 4, #47b: acceleration of system
16%
0%
4%
0%
m
or
e
in
fo
rm
(m
at
io
2g
n
)/(
m
1+
m
2)
(m
m
2g
2g
)x
(m
1+
m
2)
O
th
D
er
id
n’
tf
in
is
h
0%
d
2.
3.
4.
5.
6.
Need more
information
(m2g)/(m1+m2)
m2g
(m2g)x(m1+m2)
Other
Didn’t finish
ee
1.
80%
Attendance: What’s the most pressing
issue for today’s Congress?
32%
23%
18%
11%
7%
ca
re
q
lth
Ira
ea
H
is
a
D
at
ur
al
5%
e
st
er rgy
re
co
G
ay
...
m
ar
r ia
ge
n
En
at
io
uc
Ed
N
m
in
th
e
US
.
5%
rr
or
is
5.
6.
7.
Terrorism in the US.
Education
Energy
Natural Disaster
recovery/preparation
Gay marriage
Iraq
Health care
Te
1.
2.
3.
4.
New homework policy
• Only first and last problems are
required
• Others are optional, “bonus points”,
good practice
• New office hours for KR:
– WTh 5:30-6:30 PM in Marigold’s
Jane is traveling in a train that moves at a
constant velocity. She passes a packet of secret
documents to Bill, who is standing beside the
tracks. Bill catches the packet, which falls
straight down into his hands. Jane…
1.
2.
3.
Dropped the packet
straight down from the
window of the train
Threw the packet
towards the front of the
train
Threw the packet
towards the back of the
train
A car is moving in the +x direction at constant
speed. Which of the following is true?
25% 25% 25% 25%
1.
2.
3.
70
4.
The net force on the car is
in the +x direction.
The net force on the car is
zero
There is a net force on the
car due to gravity, in the
“down” direction
Need more information
n
m
or
e
ne
a
N
ee
d
is
re
in
fo
rm
at
io
...
on
tf
or
ce
th
e
on
he
ne
he
Th
e
ne
0
tf
or
ce
tf
or
ce
on
th
e
ca
c.
.
...
0
10
A car rounds a curve while maintaining a
constant speed. Is there a net force on
the car as it rounds the curve?
93%
1. No. Its speed is
constant.
2. Yes
3. Depends on the
sharpness of the
curve and the
speed of the car
4%
ep
D
N
o.
Its
sh
ar
...
en
ds
sp
ee
on
d
is
th
e
co
ns
t
...
Ye
s
2%
You are a passenger in a car and not wearing
your seat belt. Without changing speed, the car
makes a sharp left turn. Which of the following
is correct?
78%
18%
4%
of
th
e
a.
..
...
ab
e
on
N
B
ot
h
of
th
e
th
e
tu
rn
,..
.
0%
tu
rn
...
th
e
ur
in
g
D
3.
4.
ur
in
g
2.
During the turn, there is a
rightward force pushing you into
the door.
During the turn, the door exerts
a leftward force on you.
Both of the above.
None of the above.
D
1.
A constant force is exerted on a cart that is
initially at rest on an air track. (Ignore
friction). The force acts for a short time
interval and gives the cart a final speed. To 10
reach the same final speed with a force that is
only half as big, the force must be exerted on
the cart for a time interval:
20% 20% 20% 20% 20%
ur
..that for the
stronger force.
tim
es
Tw
as
ic
e
...
as
lo
ng
a
Eq s
H
ua
al
lt
fa
o
s
lo
ng
A
as
qu
ar
te
ro
f
Four times as long as
Twice as long as
Equal to
Half as long as
A quarter of
Fo
0
of
70
1.
2.
3.
4.
5.
A constant force is exerted on a cart that is
initially at rest on an air track. (Ignore
friction). The force acts for a short time
interval and gives the cart a final speed. The 10
same force is exerted for the same length of
time on another cart, also initially at rest, that
has twice the mass of the first one. The final
speed of the heavier cart is:
One fourth
Four times
Equal to
Half as large as
double
ub
le
rg
e
la
s
lf
a
do
as
o
lt
ua
Eq
tim
es
rth
ur
Fo
fo
u
ne
..that for the
lighter cart.
20% 20% 20% 20% 20%
O
0
of
70
1.
2.
3.
4.
5.
A constant force is exerted on a cart that is initially at
rest on an air track (as before). Suppose we repeat the
experiment but instead of starting from rest, the cart
is already moving with constant speed in the direction of10
the force at the moment we begin to apply the force.
After we exert the same constant force for the same
short time interval, the increase in the cart’s speed:
t..
.
de
as
...
r..
.
be
nn
ot
he
sa
m
e
o
fo
u
...
th
e
o
eq
ua
lt
ic
...
tw
ua
lt
5.
o
4.
eq
0
of
70
ua
lt
3.
Is equal to twice its initial speed
20% 20% 20% 20% 20%
Is equal to the square of the
initial speed
Is equal to four times its initial
speed
Is the same as when it started
from rest
Cannot be determined from the
info given
eq
1.
2.
A car was found off the side of the road. When
the police investigate, they notice cargo piled
up against the passenger-side wall. What can 10
they conclude about what happened to the car?
as
...
It
di
d
n’
t
sp
i
n
of
ft
he
...
...
sp
un
It
0
of
70
of
ft
he
3.
sp
un
2.
It spun off the road clockwise as33% 33% 33%
viewed from above
It spun off the road
counterclockwise as viewed from
above.
It didn’t spin as it went off the
road.
It
1.