Physics Chapter 2
(a) Can the instantaneous velocity of an object at an instant of time ever be greater in magnitude than the average velocity over a time interval containing that instant? (b) Can it ever be less?
(a) Yes. (b) Yes.
(a) Can the equations in Table 2.4 (pg. 38) be used in a situation where the acceleration varies with time? (b) Can they be used when the acceleration is zero?
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A ball rolls in a straight line along the horizontal direction. Using motion diagrams (or multi-flash photographs), describe the velocity and acceleration of the ball for each of the following situations: (a) The ball moves to the right at a constant speed. (b) The ball moves from right to left and continually slows down. (c) The ball moves from right to left and continually speeds up. (d) The ball moves to the right, first speeding up at a constant rate and then slowing down at a constant rate.
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If the velocity of a particle is zero, can the particle's acceleration be nonzero? Explain.
Yes. An object thrown vertically upward upon reaching its maximum height will momentarily stop at the top. At this point, the velocity is zero. However, the object's acceleration, (which is 9.8 m/s^2 downward) is NOT zero. To say that the acceleration is zero is like saying that gravity is turned off just because the object has reached a maximum height. It is because of this downward acceleration of the object that it finally stops at its highest point after which it goes down.
If the velocity of a particle is nonzero, can the particle's acceleration be zero? Explain.
Yes. If the velocity of the particle is nonzero, the particle is in motion. If the acceleration is zero, the velocity of the particle is unchanging or constant.
If a car is traveling eastward, can its acceleration be westward? Explain.
Yes. If this occurs, the acceleration of the car is opposite to the direction of motion, and the car will be slowing down.
Consider the following combinations of signs and values for the velocity and acceleration of a particle with respect to a one-dimensional x-axis (first #= velocity, second # = acceleration). a. Positive, Positive b. Positive, Negative c. Positive, Zero d. Negative, Positive e. Negative, Negative f. Negative, Zero g. Zero, Positive h. Zero, Negative Describe what the particle is doing in each case and give a real-life example for an automobile on an east-west one dimensional axis, with east considered the positive direction.
a. the car is moving to the east and speeding up b. the car is moving to the east but slowing down c. the car is moving to the east at a constant speed d. the car is moving to the west but slowing down e. the car is moving to the west and speeding up f. the car is moving to the west at a constant speed g. the car starts from rest and begins to speed up toward the east h. the car starts from rest and begins to speed up toward the west
A ____ quantity is characterized by both a magnitude and a direction. A ____ quantity has a magnitude only.
vector; scalar
