HPHY 154 Workout 08
Work
Prof. A. E. Bak
Name
Work is the effect of force acting over displacement. For a force
f
acting over a path
C
of
displacement, the work
W
done is defined by
W
!
"
C
f
!
dl
,
where
dl
is an infinitesimal displacement along
C
. For a constant force acting over a displacement
D
,
this definition yields simply
W
!
f
!
D
!
fD
cos
!
,
where
!
is the tailtotail angle between
f
and
D
.
1.
S&J Problem 72 (formerly S&B Problem 72). A shopper in a supermarket pushes a cart with a
35.0N force directed at an angle of 25.0
#
below the horizontal. Find the work done by the
shopper as he moves down an aisle 50.0
m
long.
2.
In order to push a 25.0
kg
crate up a frictionless incline, angled at 25.0
#
to the horizontal, you
exert a 209N force parallel to the incline. As the crate slides 1.50
m
, what work is done on the
crate by:
a.
you.
b.
the gravitational force.
c.
the normal force exerted by the incline.
3.
S&J Problem 720 (formerly S&B Problem 725). As shown in Figure
P
7.20 (on page 211), a
small mass
m
is pulled to the top of a frictionless halfcylinder of radius
R
by a cord that passes
over the top of the halfcylinder.
a.
If the mass moves at constant speed, then show that
f
!
mg
cos
!
.
Hint:
The tangential
acceleration
a
s
is zero here.
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 Spring '08
 stevens
 Force, Mass, Work, appropriate SI units, Prof. A. E. Bak

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