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| PAGE: 173 | SET: Exercises | PROBLEM: 1 |
The function is 
.
(a)
Find the velocity at time 
:
The motion of the particle is 
, where 
is in seconds and 
is measured in feet.
Velocity function is derivative of the position function and is defined as 
.
.
Velocity at time is 
.
(b)
Find the velocity after 
sec :
Velocity function is 
.
Substitute 
in above expression.
Velocity after 
seconds is 
ft/sec.
(c)
Find the time when particle is at rest.
Velocity function is .
When the particle is at rest, the initial velocity is zero.
.
and 
.
The particle is at rest when sec and sec.
(d)
Find the time when the particle move in positive direction.
Velocity function is .
When the particle is at rest, the initial velocity should be greater than zero.
.
The above inequality is true, when both factors are positive or both factors are negative.
If both factors are positive, then 
and 
.
It is concluded that 
.
If both factors are negative, then 
and 
.
It is concluded that 
.
The particle moves in positive direction when 
and 
.
(e)
Find the distance traveled by particle in 
sec.
The time intervals are 
, 
and 
from (d).
Find the distance traveled by the particle in the interval .
The function is .
.
.
Find the distance traveled by the particle in the interval .
.
Find the distance traveled by the particle in the interval .
.
.
Total distance is 
ft.
(f)
The schematic diagram of motion of the particle is
(g)
Find the acceleration at time and after sec.
Acceleration is derivative of the velocity function.
Velocity function is .
The acceleration at time is 
Acceleration after sec :
Substitute in the acceleration.
Acceleration after sec is 
.
(h)
Graph :
Graph the position, velocity and acceleration functions for 
.
.gif)
.
(i)
The particle speeds up when the velocity is positive and increasing.
Thus, from the graph it happens in the interval .
The particle also speeds up when the velocity is negative and decreasing.
Thus, from the graph it happens in the interval 
.
The particle slows down when the velocity and acceleration have opposite signs.
Thus, from the graph it happens in the interval 
or 
.
(a) Velocity at time is .
(b) Velocity after seconds is ft/sec.
(c) The particle is at rest when sec and sec.
(d) The particle moves in positive direction when 
and .
(e) Distance traveled in first 
sec is 
ft.
(f) The schematic diagram of motion of the particle is
(g) Acceleration after sec is 
.
(h)
(i)
When the particle speeds up in the interval 
or .
When the particle slows down in the interval 
or 
.
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