Page 138 Practice Problem 5.14: If, instead of the fish, we place a 3.00 kg rock in the pan, how much does the spring stretch? Answer: twice as much, 2.45 cm.

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Chapter14: Static Equilibrium, Elasticity, And Fracture
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140 CHAPTER 5 Applications of Newton's Laws
EXAMPLE 5.14 Fishy business
In this example we will consider the forces that come into play in a spring balance. Suppose that a spring
balance used to weigh fish is built with a spring that stretches 1.00 cm when a 12.0 N weight is placed in the
pan. When the 12.0 N weight is replaced with a 1.50 kg fish, what distance does the spring stretch?
SOLUTION
SET UP Figure 5.22a and b shows how the spring responds to the
12.0 N weight and to the 1.50 kg fish. The spring and fish are in equi-
librium. We draw a free-body diagram for the fish (Figure 5.22c), show-
ing the downward force of gravity and the upward force exerted by the
stretched spring. We point the y axis vertically upward, as usual.
SOLVE We want to use Hooke's law (Fspr= kAL) to relate the stretch
of the spring to the force, but first we need to find the force constant k.
The problem states that forces of magnitude 12.0 N are required to
stretch the spring AL = 1.00 cm (= 1.00 × 10-2 m), so
bo
1200 N/m.
k=
12.0 N
1.00 × 102 m
► FIGURE 5.22 Weighing a fish.
the che
AL= 1.00 cm
adi
Charson22
svitie
--X
12.0 N
(a) The scale stretched by a
known weight
The weight of the 1.50 kg fish is
w = mg =
(1.50 kg) (9.80 m/s²)
The equilibrium condition for the fish is
50169 31 115)
and finally, AL = 0.0123 m = 1.23 cm.
REFLECT The weight of the fish is greater than the amount of force
needed to stretch the spring 1.00 cm, so we expect the fish to stretch the
spring more than 1.00 cm.
-mg + Fspr = 0,
ΣΕ, = 0,
-14.7 N+ (1200 N/m) AL = 0,
Practice Problem: If, instead of the fish, we place a 3.00 kg rock in the
pan, how much does the spring stretch? Answer: twice as much, 2.45 cm.
ute etter
AL="
38380
///////////z
m = 1.50 kg
w = mg
Video Tutor Solut
= 14.7 N.
(b) The scale stretched by a
known mass
Fspr
W = mg
(c) Free-body diagram
for the fish
REF
are i
is th
that
5.5
Th
tu
fr
u
Transcribed Image Text:140 CHAPTER 5 Applications of Newton's Laws EXAMPLE 5.14 Fishy business In this example we will consider the forces that come into play in a spring balance. Suppose that a spring balance used to weigh fish is built with a spring that stretches 1.00 cm when a 12.0 N weight is placed in the pan. When the 12.0 N weight is replaced with a 1.50 kg fish, what distance does the spring stretch? SOLUTION SET UP Figure 5.22a and b shows how the spring responds to the 12.0 N weight and to the 1.50 kg fish. The spring and fish are in equi- librium. We draw a free-body diagram for the fish (Figure 5.22c), show- ing the downward force of gravity and the upward force exerted by the stretched spring. We point the y axis vertically upward, as usual. SOLVE We want to use Hooke's law (Fspr= kAL) to relate the stretch of the spring to the force, but first we need to find the force constant k. The problem states that forces of magnitude 12.0 N are required to stretch the spring AL = 1.00 cm (= 1.00 × 10-2 m), so bo 1200 N/m. k= 12.0 N 1.00 × 102 m ► FIGURE 5.22 Weighing a fish. the che AL= 1.00 cm adi Charson22 svitie --X 12.0 N (a) The scale stretched by a known weight The weight of the 1.50 kg fish is w = mg = (1.50 kg) (9.80 m/s²) The equilibrium condition for the fish is 50169 31 115) and finally, AL = 0.0123 m = 1.23 cm. REFLECT The weight of the fish is greater than the amount of force needed to stretch the spring 1.00 cm, so we expect the fish to stretch the spring more than 1.00 cm. -mg + Fspr = 0, ΣΕ, = 0, -14.7 N+ (1200 N/m) AL = 0, Practice Problem: If, instead of the fish, we place a 3.00 kg rock in the pan, how much does the spring stretch? Answer: twice as much, 2.45 cm. ute etter AL=" 38380 ///////////z m = 1.50 kg w = mg Video Tutor Solut = 14.7 N. (b) The scale stretched by a known mass Fspr W = mg (c) Free-body diagram for the fish REF are i is th that 5.5 Th tu fr u
Page 138 Practice Problem 5.14:
If, instead of the fish, we place a 3.00 kg rock in the pan, how much does the
spring stretch? Answer: twice as much, 2.45 cm.
Transcribed Image Text:Page 138 Practice Problem 5.14: If, instead of the fish, we place a 3.00 kg rock in the pan, how much does the spring stretch? Answer: twice as much, 2.45 cm.
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