Physics Ch. 2

Starting from rest, a car accelerates down a straight road with constant acceleration a for a time t, then the direction of the acceleration is reversed, i.e., it is -a, and the car comes to a stop in an additional time t, the time for the whole trip being 2t. At what time, or times, is the average velocity of the car for the trip equal to its instantaneous velocity during the trip?

This occurs at 2 times, 0.5t and 1.5t

Which of the following is not a vector quantity?

temperature

An object moves 20 m east in 30 s and then returns to its starting point taking an additional 50 s. If west is chosen as the positive direction, what is the sign associated with the average velocity of the object?

0 (no sign)

In which of the following cases is the displacement's magnitude half the distance traveled?

15 steps east followed by 5 steps west

A ball rolls down an incline, starting from rest. If the total time it takes to reach the end of the incline is T, how much time has elapsed when it is halfway down the incline?

> 0.5 T

Two objects of different mass are released simultaneously from the top of a 20-m tower and fall to the ground. If air resistance is negligible, which statement best applies?

Both objects hit the ground together

In one-dimensional motion where the direction is indicated by a plus or minus sign, the average velocity of an object has which of the following properties?

It can be positive, negative, or zero

A ball of relatively low density is thrown upwards. Because of air resistance the acceleration while traveling upwards is -10.8 m/s2. On its trip downward the resistance is in the opposite direction and the resulting acceleration is -8.8 m/s2. When the ball reaches the level from which it was thrown, how does its speed compare to that with which it was thrown?

It is less than the original speed upward

In one-dimensional motion, the average speed of an object that moves from one place to another and then back to its original place has which of the following properties?

It is positive

Jeff throws a ball straight up. For which situation is the vertical velocity zero?

at the top

A baseball catcher throws a ball vertically upward and catches it in the same spot when it returns to his mitt. At what point in the ball's path does it experience zero velocity and non-zero acceleration at the same time?

at the top of its trajectory

On a position versus time graph, the slope of the straight line joining two points on the plotted curve that are separated in time by the interval t, is which of the following quantities?

average velocity

In the case of constant acceleration, the average velocity equals the instantaneous velocity:

half-way through the time interval

An object is dropped from a height. Once it is moving, which of the following statements is true, at least at one point?

its velocity is never equal to its acceleration

If the displacement of an object is given in SI units by x = -3 t + 4 t 2, at t = 2 s its velocity and acceleration are, respectively:

positive, positive

The value of an object's acceleration may be characterized in equivalent words by which of the following?

rate of change of velocity

A strobe photograph shows equally spaced images of a car moving along a straight road. If the time intervals between images is constant, which of the following cannot be positive?

the acceleration of the car

A strobe photograph of a car moving along a straight road shows the interval between each successive image to be diminishing. If the direction of motion of the car is taken as positive, which of the following are negative?

the average acceleration of the car

An x vs. t graph is drawn for a ball moving in one direction. The graph starts at the origin and at t = 5 s the velocity of the ball is zero. We can be positive that at t = 5 s,

the ball has stopped

The slope of the acceleration vs. time curve represents:

the rate of change of acceleration

A v vs. t graph is drawn for a ball moving in one direction. The graph starts at the origin and at t = 5 s the acceleration of the ball is zero. We know that at t = 5 s,

the velocity of the ball is not changing

A change in a physical quantity w having initial value wi and final value wf is given by which of the following?

wf - wi

Changing the positive direction in a reference frame to the opposite direction does not change the sign of which of the following quantities?

Speed

Displacement is which of the following types of quantities?

Vector

Starting from rest, a car accelerates down a straight road with constant acceleration a1 for a time t1, then the acceleration is changed to a different constant value a2 for an additional time t2. The total elapsed time is t1 + t2. Can the equations of kinematics be used to find the total distance traveled?

Yes, break the problem up into 2 problems, one with the conditions for the first time interval and the other with the conditions for the second time interval, noting that for the second time interval the initial velocity is that from the end of the first time interval. when done, add the distances from each of the time intervals