College Physics
College Physics
11th Edition
ISBN: 9781305952300
Author: Raymond A. Serway, Chris Vuille
Publisher: Cengage Learning
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Question
If the car in example 2.5 maintains its constant acceleration for a total time of 10s, what total distance does it travel? Answer 250m Both images have background info to solve the practice problem.
e of
od-
als
Px
t
We call the position at time =0 the initial position, denoted by xo. The position at the
later time is simply x. Thus, for the time interval A = 0 and the corresponding dis-
placement x-xo. the general definition gives
CAFE
(2.9)
Vav, x
Finally, we equate Equations 2.8 and 2.9 and simplify the result to obtain the following
equation:
.
x - хо
t
Position as a function of time for an object moving with constant acceleration
For an object undergoing constant acceleration, its position at some time t is given by
x = xo + vot + ½a,1².
(2.10)
Units: The units of each of the three terms on the right-hand side reduce to meters.
Notes:
xo is the position at t = 0.
• Vor is the velocity at t = 0.
• ay is the acceleration, which is assumed to be constant in time.
x is the position at some later time t.
100 05/12 19
EXAMPLE 2.6 Passing distance
Let's now revisit Example 2.5 and calculate how far the car travels during its 5.0 s of acceleration.
SOLUTION
SET UP We use the same coordinates as in Example 2.5. As before,
Vax=+15 m/s and a = +2.0 m/s².
SOLVE We want to solve for x-xo, the distance traveled by the car
during the 5.0 s time interval. The acceleration is constant, so we can
use Equation 2.10 to find
x = xo = voxt + axt²
Video Tutor Solution
(15 m/s) (5.0 s) + (2.0 m/s²) (5.0 s)²
= 75 m + 25 m = 100 m.
CONTINUED
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Transcribed Image Text:e of od- als Px t We call the position at time =0 the initial position, denoted by xo. The position at the later time is simply x. Thus, for the time interval A = 0 and the corresponding dis- placement x-xo. the general definition gives CAFE (2.9) Vav, x Finally, we equate Equations 2.8 and 2.9 and simplify the result to obtain the following equation: . x - хо t Position as a function of time for an object moving with constant acceleration For an object undergoing constant acceleration, its position at some time t is given by x = xo + vot + ½a,1². (2.10) Units: The units of each of the three terms on the right-hand side reduce to meters. Notes: xo is the position at t = 0. • Vor is the velocity at t = 0. • ay is the acceleration, which is assumed to be constant in time. x is the position at some later time t. 100 05/12 19 EXAMPLE 2.6 Passing distance Let's now revisit Example 2.5 and calculate how far the car travels during its 5.0 s of acceleration. SOLUTION SET UP We use the same coordinates as in Example 2.5. As before, Vax=+15 m/s and a = +2.0 m/s². SOLVE We want to solve for x-xo, the distance traveled by the car during the 5.0 s time interval. The acceleration is constant, so we can use Equation 2.10 to find x = xo = voxt + axt² Video Tutor Solution (15 m/s) (5.0 s) + (2.0 m/s²) (5.0 s)² = 75 m + 25 m = 100 m. CONTINUED
42
CHAPTER 2 Motion Along a Straight Line
REFLECT If the speed were constant and equal to the initial value
Vo 15 m/s, the car would travel 75 m in 5.0 s. It actually travels
farther because the speed is increasing. From Example 2.5, we know
that the final velocity is u, 25 m/s, so the average velocity for the
5.0 s segment of motion is
Vox + Ux
2
Uav,x=
15 m/s + 25 m/s 20 m/s.
2
An alternative way to obtain the distance traveled is to multiply
the average velocity by the time interval. When we do this, we get
x-xo=Uav.x = (20 m/s) (5.0 s) = 100 m, the same result we
obtained using Equation 2.10.
Practice Problem: If the car in Example 2.5 maintains its constant
acceleration for a total time of 10 s, what total distance does it travel?
Answer: 250 m.
For some problems, we aren't given the time interval for the motion, and we need to
obtain a relationship for x, Ux, and a, that doesn't contain t. To obtain such a relationship,
we can combine Equations 2.6 and 2.10 to eliminate t. This involves a little algebra, but the
result is worth the effort!
t =
We first solve Equation 2.6 for t and then substitute the resulting expression into Equa-
tion 2.10 and simplify:
UxVox
ax
x = xo + vox
Ux - Vox
ax
+
Vor) ².
ar
We transfer the term xo to the left side and multiply through by 2ax:
2ax(x xo) = 200xx - 200 + v² – 2000, + vo?.
Finally, we combine terms and simplify to obtain the following equation:
Velocity as a function of position for an object moving with constant
acceleration
uiqmie
For an object moving in a straight line with constant acceleration a,
v₂ = vor + 2ax(x - xo).
Units: The units of each term in this equation reduce to m²/s².
Notes:
(2.11)
• Vox is the initial velocity of the object when it is at its initial position xo.
• U is the final velocity of the object when it is at its final position x.
• This equation is generally used in problems that neither give a time t nor ask for one.
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Transcribed Image Text:42 CHAPTER 2 Motion Along a Straight Line REFLECT If the speed were constant and equal to the initial value Vo 15 m/s, the car would travel 75 m in 5.0 s. It actually travels farther because the speed is increasing. From Example 2.5, we know that the final velocity is u, 25 m/s, so the average velocity for the 5.0 s segment of motion is Vox + Ux 2 Uav,x= 15 m/s + 25 m/s 20 m/s. 2 An alternative way to obtain the distance traveled is to multiply the average velocity by the time interval. When we do this, we get x-xo=Uav.x = (20 m/s) (5.0 s) = 100 m, the same result we obtained using Equation 2.10. Practice Problem: If the car in Example 2.5 maintains its constant acceleration for a total time of 10 s, what total distance does it travel? Answer: 250 m. For some problems, we aren't given the time interval for the motion, and we need to obtain a relationship for x, Ux, and a, that doesn't contain t. To obtain such a relationship, we can combine Equations 2.6 and 2.10 to eliminate t. This involves a little algebra, but the result is worth the effort! t = We first solve Equation 2.6 for t and then substitute the resulting expression into Equa- tion 2.10 and simplify: UxVox ax x = xo + vox Ux - Vox ax + Vor) ². ar We transfer the term xo to the left side and multiply through by 2ax: 2ax(x xo) = 200xx - 200 + v² – 2000, + vo?. Finally, we combine terms and simplify to obtain the following equation: Velocity as a function of position for an object moving with constant acceleration uiqmie For an object moving in a straight line with constant acceleration a, v₂ = vor + 2ax(x - xo). Units: The units of each term in this equation reduce to m²/s². Notes: (2.11) • Vox is the initial velocity of the object when it is at its initial position xo. • U is the final velocity of the object when it is at its final position x. • This equation is generally used in problems that neither give a time t nor ask for one.
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