istance d from the bus, the light changes and the bus starts to move away from the running man w onstant acceleration a. When will the man catch the bus? Explain your answer. This is the distance travelled by the bus = d, Amelematian of kas a Altien f te ke Spred af the person = V

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Chapter1: Units, Trigonometry. And Vectors
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PROBLEM 5
Imagine that a man is running at his top speed v to catch a bus that is stopped at a traffic light. When he is still a
distance d from the bus, the light changes and the bus starts to move away from the running man with a
constant acceleration a. When will the man catch the bus? Explain your answer.
This is the distance travelled by the bus = d
Aliosof the
Speed of the person
The total distance travelled by a man to catch the bus = d+ d.
consider man:
Given:
x, =d+d, distance travelled by the man
consider man:
d = distance of the man to the bus
x, =v•
d+d, = v•, → eq. 1
before the bus start to move
consider bus:
v = velocity of the man
t = time of man
d, = v1+-a ·1, distance travelled by the bus
consider bus:
1,= time of the bus
=a-t → cq. 2
d, = distance travelled by the bus
substitute eq.2 to eq.1
Vi = 0 velocity initial of the bus
a = acceleration of the bus
d+a•1, =v•t, , =1,
note: time of the man is same of the bus
d+
Reg:t =? time to catch the bus
++d =0
[ 2
2v±2,(v – 2ad
a t - 2v·1+2d = 0
2a
use quadratic eq. to solve for t.
vt(v - 2ad)
ax? + bx +c = 0
2a
a = a
b = -2v
c = 2d
From here, we are only concern about
-bt Vb? - 4ac
the nature of the discriminant. If it is
2a
imaginary.
v2 - 2ad → should not be less than zero
or else we will have an imaginary value.
real
-(-2v)± (-2v)² – 4(a)(2d)
2(a)
2vtV4v - 8ad
2a
Thus, we can conclude that the man can catch the bus
2v± 4(v² – 2ad)
only if he will be able to attain a speed which will be
2a
equal to or higher that the value of sqrt(2ad).
14
Science is the belief in the ignorance of experts – Richard Feynman
Transcribed Image Text:PROBLEM 5 Imagine that a man is running at his top speed v to catch a bus that is stopped at a traffic light. When he is still a distance d from the bus, the light changes and the bus starts to move away from the running man with a constant acceleration a. When will the man catch the bus? Explain your answer. This is the distance travelled by the bus = d Aliosof the Speed of the person The total distance travelled by a man to catch the bus = d+ d. consider man: Given: x, =d+d, distance travelled by the man consider man: d = distance of the man to the bus x, =v• d+d, = v•, → eq. 1 before the bus start to move consider bus: v = velocity of the man t = time of man d, = v1+-a ·1, distance travelled by the bus consider bus: 1,= time of the bus =a-t → cq. 2 d, = distance travelled by the bus substitute eq.2 to eq.1 Vi = 0 velocity initial of the bus a = acceleration of the bus d+a•1, =v•t, , =1, note: time of the man is same of the bus d+ Reg:t =? time to catch the bus ++d =0 [ 2 2v±2,(v – 2ad a t - 2v·1+2d = 0 2a use quadratic eq. to solve for t. vt(v - 2ad) ax? + bx +c = 0 2a a = a b = -2v c = 2d From here, we are only concern about -bt Vb? - 4ac the nature of the discriminant. If it is 2a imaginary. v2 - 2ad → should not be less than zero or else we will have an imaginary value. real -(-2v)± (-2v)² – 4(a)(2d) 2(a) 2vtV4v - 8ad 2a Thus, we can conclude that the man can catch the bus 2v± 4(v² – 2ad) only if he will be able to attain a speed which will be 2a equal to or higher that the value of sqrt(2ad). 14 Science is the belief in the ignorance of experts – Richard Feynman
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