(III) Mary and Sally are in a fool race (Fig. 2-43). When Mary is 22 m from the finish line, she has a speed of 4.0 m/s and is 5.0 m behind Sally, who has a speed of 5.0 m/s. Sally thinks she has an easy win and so. during the remaining portion of the race, decelerates at a constant rate of 0.50 m/s 2 to the finish line. What constant acceleration does Mary now need during the remaining portion of the race. If she wishes to cross the finish line side-by-side with Sally? FIGURE 2-43 Problem 47. 47. For the runners to cross the finish line side-by-side means they must both reach the finish line in the same amount of time from their current positions. Take Mary's current location as the origin. Use Eq. 2-12b. For Sally: 22 = 5 + 5t + 1 2 (−.5) → t 2 − 20 t + 68 = 0 → t = 20 ± 20 2 − 4 ( 68 ) 2 = 4.343 s . 15.66 s The first time is the time she first crosses the finish line, and so is the time to be used for the problem. Now find Mary's acceleration so that she crosses the finish line in that same amount of time. For Mary: 22 = 0 + 4 t + 1 2 a t 2 → a = 22 − 4 t 1 2 t 2 = 22 − 4 ( 4.343 ) 1 2 ( 4.343 ) 2 = 0.49 m / s 2
(III) Mary and Sally are in a fool race (Fig. 2-43). When Mary is 22 m from the finish line, she has a speed of 4.0 m/s and is 5.0 m behind Sally, who has a speed of 5.0 m/s. Sally thinks she has an easy win and so. during the remaining portion of the race, decelerates at a constant rate of 0.50 m/s 2 to the finish line. What constant acceleration does Mary now need during the remaining portion of the race. If she wishes to cross the finish line side-by-side with Sally? FIGURE 2-43 Problem 47. 47. For the runners to cross the finish line side-by-side means they must both reach the finish line in the same amount of time from their current positions. Take Mary's current location as the origin. Use Eq. 2-12b. For Sally: 22 = 5 + 5t + 1 2 (−.5) → t 2 − 20 t + 68 = 0 → t = 20 ± 20 2 − 4 ( 68 ) 2 = 4.343 s . 15.66 s The first time is the time she first crosses the finish line, and so is the time to be used for the problem. Now find Mary's acceleration so that she crosses the finish line in that same amount of time. For Mary: 22 = 0 + 4 t + 1 2 a t 2 → a = 22 − 4 t 1 2 t 2 = 22 − 4 ( 4.343 ) 1 2 ( 4.343 ) 2 = 0.49 m / s 2
(III) Mary and Sally are in a fool race (Fig. 2-43). When Mary is 22 m from the finish line, she has a speed of 4.0 m/s and is 5.0 m behind Sally, who has a speed of 5.0 m/s. Sally thinks she has an easy win and so. during the remaining portion of the race, decelerates at a constant rate of 0.50 m/s2 to the finish line. What constant acceleration does Mary now need during the remaining portion of the race. If she wishes to cross the finish line side-by-side with Sally?
FIGURE 2-43 Problem 47.
47. For the runners to cross the finish line side-by-side means they must both reach the finish line in the same amount of time from their current positions. Take Mary's current location as the origin. Use Eq. 2-12b.
The first time is the time she first crosses the finish line, and so is the time to be used for the problem. Now find Mary's acceleration so that she crosses the finish line in that same amount of time.
For Mary:
22
=
0
+
4
t
+
1
2
a
t
2
→
a
=
22
−
4
t
1
2
t
2
=
22
−
4
(
4.343
)
1
2
(
4.343
)
2
=
0.49
m
/
s
2
-------*34 In Fig.2-27, a red car and a green car, identical except for the color, move toward each other in adjacent lanes and parallel to an x axis. At time t = 0, the red car is at x, = 0 and the green car is at x, = 220 m. If the red car has a constant velocity of 20 km/h, the cars pass each other at x = 44.5 m, and if it has a constant velocity of 40 km/h, they pass each other at x = 76.6 m. What are (a) the initial velocity and (b) the constant acceleration of the green car?-----I GOT THIS PART!!! THIS IS A REFERENCE.
A truck and a car travel on a straight road with equal speeds of 72km / h, when the car is 5 m behind the truck it begins to accelerate at a rate of 2.5m / s ^ 2 until it is 55 meters in front of the truck. the maximum speed reached by the car was 90 km / h, determine the minimum time that the operation takes
Can the velocity of an object be negative when its acceleration is positive? What about vice versa? If yes, give examples in each case
Chapter 2 Solutions
Physics for Scientists and Engineers, 4th Ed + Masteringphysics: Chapters 1-38
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