Physics Chapter 3
Which BEST describes what occurs when a body accelerates?
Change in velocity per unit of time
A ball is tossed with enough speed straight up so that it is in the air several seconds. Assume upward direction is positive and downward is negative. What is the change in velocity during the 2-s interval? (Careful!)
v=-20.0 m/s
What two units of measurement are necessary for describing speed?
Distance and time
Acceleration is generally defined as the time rate of change of velocity. When can it be defined as the time rate of change of speed?
When moving in a straight line, the time rate of change of speed is acceleration.
A ball is tossed with enough speed straight up so that it is in the air several seconds. Assume upward direction is positive and downward is negative. Part A What is the velocity of the ball when it reaches its highest point? Express your answer with the appropriate units. v = 0 ms SubmitMy AnswersGive Up Correct Part B What is its velocity 1 s before it reaches its highest point?
v= 10.0 m/s
What is the acceleration of a car that maintains a constant velocity of 100 km/h for 10 s?
0 km/h-s
While you are in a bus that moves at 100 km/h you walk from the back to the front at 10 km/h. What is your speed relative to the road outside?
110 km/h
A ball freely falling at 20 m/s will in the next second have a speed of ______.
30 m/s
Three balls of different masses are thrown straight upward with initial speeds as indicated. A) 8m/s - 4.9kg B) 14m/s - 1.9kg C) 2m/s - 0.7kg From greatest to least, rank the accelerations of the balls 1 s after being thrown. Or are the accelerations the same?
All are the same
What exactly is meant by a "freely falling" object?
An object in free fall falls under gravity alone with no friction.
Average Speed
Average speed = total distance covered / time interval
Distance Traveled
Average speed x time of travel
How can you use the graph of velocity versus time to estimate the acceleration of the ball?
By estimating the value of the slope of the graph
Three balls of different masses are thrown straight upward with initial speeds as indicated. A) 8m/s - 4.9kg B) 14m/s - 1.9kg C) 2m/s - 0.7kg From fastest to slowest, rank the speeds of the balls 1 s after being thrown.
C, B, A
Suppose that a freely falling object were somehow equipped with a speedometer. By how much would its reading in speed increase with each second of fall?
Each second, the object would fall 10m/s faster than at the previous second.
Acceleration
How quickly and in what direction velocity changes; rate at which speed changes A = change of velocity / time interval
A speedometer normally measures ______.
Instantaneous speed
Light travels in a straight line at a constant speed of 300,000 km/s. What is the acceleration of light?
Since light travels at a constant speed, this would mean that there is no increase or decrease in speed. Because of this, the acceleration would then be zero.
Speed
The distance covered per unit of time; speed = Distance/time
In the video, Dr. Hewitt drops a book and a flat piece of paper together from the same height, and one object hits the ground before the other. Why does that object hit the ground first?
The heavier object--the book--hits the ground first because the other, lighter, object is more influenced by air resistance.
As you read this in your chair, how fast are you moving relative to the chair? Relative to the Sun?
You are not moving relative to the chair, but you are moving over 100,000 km/h relative to the Sun.
Select the correct equations that show that the acceleration of a hamster is 5 m/s2 when it increases its velocity from rest to 10 m/s in 2 s.
a=Δv/t=(10m/s)/(2s)=5m/s2
In the video, Dr. Hewitt drops a book and a flat piece of paper together from the same height. Which object that hits the ground first?
The book
A ball is tossed with enough speed straight up so that it is in the air several seconds. Assume upward direction is positive and downward is negative. What is the acceleration of the ball at the moment the ball has zero velocity?
a= -10.0m/s^2
A ball is tossed with enough speed straight up so that it is in the air several seconds. Assume upward direction is positive and downward is negative. What is the acceleration of the ball during any of these time intervals?
a=-10.0m/s^2
Select the correct equations that show that a freely falling rock drops a distance of 45 m when it falls from rest for 3 s .
s=g⋅t2/2=(10m/s2)⋅(3s)2/2=45m
Galileo discovered that when air resistance can be neglected, all objects fall with the same ______.
Acceleration
You are driving north on a highway. Then, without changing speed, you round a curve and drive east. Does your velocity change? Do you accelerate? Explain.
The velocity changes because your direction changes and if your velocity changes then you will also accelerate as well.
What kind of speed is registered by an automobile speedometer?
Instantaneous speed
A ball is tossed with enough speed straight up so that it is in the air several seconds. Assume upward direction is positive and downward is negative. What is the velocity of the ball when it reaches its highest point?
v=0 m/s
Select the correct equations that show that the average speed of a rabbit that runs a distance of 45 m in a time of 3 s is 15 m/s .
v=s/t=(45m)/(3s)=15m/s
When we are talking about how quickly "how fast" changes, we're talking about ______.
Acceleration
When Dr. Hewitt drops a book and a crumpled piece of paper together from the same height, which object hits the ground first, and why?
Both objects hit the ground at the same time because air resistance is negligible.
Based on the experiment that Dr. Hewitt demonstrated in the video, what factors determine whether the air resistance experienced by a falling object will affect the motion of the object?
The area of the object in relation to the weight of the object determines the air resistance the object experiences. Objects having greater area but smaller weight experience greater effect of air resistance.
Displacement
A change of position; (X final-X initial); how far, which way; EX:started at 60m, ended at 40m so, 40-60=-10 (moved in the negative direction)
Why does the distance traveled by the ball in each half second after it is released change in the way in which it does?
Gravity is pulling down on the ball, so it accelerates down at a steady rate.
What is the distance fallen for a freely falling object 1 s after being dropped from a rest position? What is the distance for a 4-s drop?
It falls 5 m in 1 s and 80 m in 4 s.
How does the distance traveled by the ball in the second half second compare with the distance traveled by the ball in the first half second?
It increases
What is the value of the velocity of the ball when it reaches its maximum height?
It is always zero
If a car is moving at 90 km/h and it rounds a corner, also at 90 km/h, does it maintain a constant speed? A constant velocity?
It maintains a constant speed, but does not maintain a constant velocity.
The difference between speed and velocity involves ______
Direction
What is the acceleration of the ball when it is moving up, when it is at the maximum height, and when it is moving down? (Note: The acceleration graph is shown in red.)
It is always negative The acceleration due to gravity is always 10 m/s^2 downward. In other words, it is -10 m/s^2
Free Fall
Motion under the influence of gravity alone
Instantaneous Speed
The speed at any instant
Velocity
The speed of an object and its direction of motion; a vector quantity
Surprisingly, very few athletes can jump more than 2 feet (0.6 m) straight up. Use d=1/2gt2 and solve for the time one spends moving upward in a 0.6-m vertical jump. Then double it for the "hang time"-the time one's feet are off the ground. Express your answer to two significant figures and include the appropriate units.
t = 0.70 s
A ball is tossed with enough speed straight up so that it is in the air several seconds. Assume upward direction is positive and downward is negative. What is the change in its velocity during this 1-s interval?
v= -10.0 m/s
What relationship between distance traveled and time did Galileo discover for freely falling objects released from rest?
Galileo discovered that distance increased as the time squared.