wednesday, 12/10/14physics if you do the same old things, you get the same old results!
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Wednesday, 12/10/14 PHYSICS
If you do the same old things,you get the same old results!
Wednesday 12/10/14 PHYSICS
ex. 1
Work, Energy, Power, and Momentumdefn. Work (W) – work done by a force is the
product of the displacement and the component of the force in the direction of the displacement.
NOTE: Work is a SCALAR quantity!
UNITS: 1Nm = 1 J (joule)
To get joules,you must use kg,m, and s.
(Usually, just W = Fdcos θ.)
Wednesday 12/10/14 PHYSICS
ex. 2 A 5.0kg crate is dragged 10.0m across a floor by a 12N force applied at 30.0º above horizontal.a) Find the work done by the force.b) If a constant frictional force of 8.4N exists, find the work done by friction.
θ is the angle between the force and the displacement!!!Forces that are perpendicular to displacement do NO work (cos 90 = 0)!!
ex. 3 How much work must a person do to lift a 49kg crate a distance of 10.0m straight up at constant speed?
defn. power (P) – the rate at which work is done
P = W/t P – power W – work t – time
UNITS: J/s = W (watts)sometimes horsepower (hp)1 hp = 746W
ex. 4 p. 181 #5 1500kg car accelerates uniformly from rest to 10.0m/s in 3.00s.a) What is the (net) work done on the car in this time interval?b) What is the (net) power delivered in this time interval.
HW 26: ws. 2, 7 – 15 odd
HW
24
HW
24
7) 6
300J
9) 6
0°11
) a)
715
N
b)
10,
000J
Th
urs
day
, 11/
29/1
2ex
. 1
ex. 2
A 5
.0k
g cr
ate
is d
ragg
ed 1
0.0m
acr
oss
a fl
oor
by
a 12
N f
orce
ap
pli
ed a
t 30
.0º
abov
e h
oriz
onta
l.a)
Fin
d t
he
wor
k d
one
by
the
forc
e.b
) I
f a
con
stan
t fr
icti
onal
for
ce o
f 8.
4N
exis
ts, f
ind
th
e w
ork
don
e b
y fr
icti
on.
ex. 3
How
mu
ch w
ork
mu
st a
per
son
do
to
lift
a 4
9kg
crat
e a
dis
tan
ce o
f 10
.0m
str
aigh
t u
p a
t co
nst
ant
spee
d?
ex. 4
p. 1
81 #
5
1500
kg
car
acce
lera
tes
un
ifor
mly
fro
m r
est
to 1
0.0m
/s in
3.0
0s.
a) W
hat
is t
he
(net
) w
ork
don
e on
th
e ca
r in
th
is t
ime
inte
rval
?b
) W
hat
is t
he
(net
) p
ower
del
iver
ed in
th
is
tim
e in
terv
al.
HW
26
HW
24
7) 6
300J
9) 6
0°11
) a)
715
N
b)
10,
000J
HW
26
HW
24
7) 6
300J
9) 6
0°11
) a)
715
N
b)
10,
000J