Portland State University Andres La Rosa PH-211

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 )

10

4

3

5 1 2

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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.