Portland State University
PH-211
Andres La Rosa
Practice Problems
17. The position of a particle moving along the x axis is given in centimeters by x
= 9.75 + 1.50 t3, where t is in seconds. Calculate
(a) the average velocity during the time interval t = 2.00 s to t = 3.00 s;
(b) the instantaneous velocity at t = 2.00 s;
(c) the instantaneous velocity at t = 3.00 s;
(d) the instantaneous velocity at t = 2.50 s; and
(e) the instantaneous velocity when the particle is midway between its
positions at t = 2.00 s and t = 3.00 s.
(f) Graph x versus t and indicate your answer graphically.
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Problem: The graph shown is for an armadillo that scampers left (negative direction) and
right (positive direction) along an x-axis. A) When, if ever, is the animal to the left of the
origin on the axis?
When, if ever, is the velocity b) negative, c) positive, or d) zero?
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69. How far does the runner whose velocity–time graph is shown in the figure
travels in 16 s?
67 )
3
1
2
4
5
10
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32. A world’s land speed record was set by Colonel John P. Stapp when in March 1954 he
rode a rocket-propelled sled that moved along a track at 1020 km/h. He and the sled
were brought to a stop in 1.4 s. In terms of g, what acceleration did he experience
while stopping?
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54. A stone is dropped into a river from a bridge 43.9 m above the water.
Another stone is thrown vertically down 1.00 s after the first is dropped.
The stones strike the water at the same time.
(a) What is the initial speed of the second stone?
(b) Plot velocity versus time on a graph for each stone, taking zero time
as the instant the first stone is released.
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Practice problem
A ball is thrown upwards with vo = 10 m/s from a height of 1 m.
a) Make a graph of Y vs t
Correct way
But, as far as we keep “y” in meters and “t” in seconds, we can write:
Simplified way
)
b) How long does it take for the ball to reach the maximum height?
(We will call that time t=t1)
e
c) What is the max height reached by the ball?
d) What is the position of the ball when t = 2t1 ?
Notice:
t1 : time it takes the ball to reach its max height
2t1 : time it takes the ball to come back to its initial height.