1
Chap. 2 HW
– part 1
Questions
2.
Figure 215 is a graph of a particle’s position along an
x
axis
versus time.
(a) At time
t
=
0, what is the sign of the particle’s position?
At
t
= 0,
x
is
negative
Is the particle’s velocity positive, negative, or 0 at:
(b)
t
= l s,
At
t
= 1s,
v
is positive (
v
= d
x
/d
t
, at slope of curve which
is positive)
(c)
t
=2 s,
At
t
= 2s,
v
is 0 (slope of
x
vs
t
is 0)
(d)
t
= 3 s?
At
t
= 3s,
v
is negative (slope of
x
vs
t
is )
(e) How many times does the particle go through the point
x
=
0?
Two times (at
t
= 1 sec and
t
= 3 sec)
3.
Figure 216 gives the velocity of a particle moving along an
axis.
Point 1 is at the highest point on the curve; point 4 is at
the lowest point; and points 2 and 6 are at the same height.
What is the direction of travel at
(a) time
t
= 0
At
t
= 0,
v
is + so direction is along the positive axis
(b) 4?
At
t
= 4 s,
v
is  so direction is along the negative axis
(c) At which of the six numbered points does the particle reverse its direction of travel?
Particle reverses its direction when
v
changes sign, i.e. at
t
= 3 s and 5 s.
(d) Rank the six points according to the magnitude of the acceleration, greatest first.
Acceleration is equal to the
slope
of the
v
vs
t
curve:
Largest for
t
= 2, 6, smaller for
t
= 3, 5 and zero for
t
= 1, 4 s.
Problem
2.
The 1992 world speed record for a bicycle (human powered vehicle) was set by Chris Huber.
His time through the measured 200 m stretch was a sizzling 6.509 s, at which he commented,
“Cogito ergo zoom!” (I think, therefore I go fast!).
In 2001, Sam Whittingham beat Huber’s
record by 19.0 km/h.
What was Whittingham’s time through the 200 m?
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 Spring '08
 oshea
 Acceleration, Velocity, San Antonio, km/h

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