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Physics 2211-001, Fall 2008
Newton's third Law
Due at 11:00pm on Wednesday, September 17, 2008
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Position, Velocity, and Acceleration
Learning Goal:
To identify situations when position, velocity, and /or acceleration change, realizing that change
can be in direction or magnitude.
If an object's position is described by a function of time,
(measured from a nonaccelerating reference frame), then
the object's velocity is described by the time derivative of the position,
, and the object's acceleration is
described by the time derivative of the velocity,
.
It is often convenient to discuss the average of the latter two quantities between times
and
:
and
.
Part A
You throw a ball. Air resistance on the ball is negligible. Which of the following functions change with time as the
ball flies through the air?
Hint A.1
Newton's 2nd Law
Hint not displayed
ANSWER:
only the position of the ball
only the velocity of the ball
only the acceleration of the ball
the position and velocity of the ball
the position and the velocity and acceleration of the ball
Part B
You are driving a car at 65 mph. You are traveling north along a straight highway. What could you do to give the car
a nonzero acceleration?
Hint B.1
What constitutes a nonzero acceleration?
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Hint not displayed
ANSWER:
Press the brake pedal.
Turn the steering wheel.
Either press the gas or the brake pedal.
Either press the gas or the brake pedal or turn the steering wheel.
Part C
A ball is lodged in a hole in the floor near the outside edge of a merry-go-round that is turning at constant speed.
Which kinematic variable or variables change with time, assuming that the position is measured from an origin at
the center of the merry-go-round?
Hint C.1
Change of a vector
Hint not displayed
ANSWER:
the position of the ball only
the velocity of the ball only
the acceleration of the ball only
both the position and velocity of the ball
the position and velocity and acceleration of the ball
Part D
For the merry-go-round problem, do the magnitudes of the position, velocity, and acceleration vectors change with
time?
Hint D.1 Change of magnitude of a vector
Hint not displayed
ANSWER:
yes
no
Problem 7.9
To withstand "g-forces" of up to 10 g's, caused by suddenly pulling out of a steep dive, fighter jet pilots train on a
"human centrifuge." 10 g's is an acceleration of
.
Part A
If the length of the centrifuge arm is 10.0
, at what speed is the rider moving when she experiences 10 g's?
ANSWER:

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