Chapter 8, Science
a train traveling at 30 m/s brakes to a stop in 1 minute, its acceleration is _________.
-0.5 m/s2
What is the acceleration of the ball between 0 and 3 seconds?
1 m/s2 (3m/s - 0 m/s)/3 s = (3 m/s)/(3 s) = (1 m/s)/s = 1 m/s2
How long after Kathy started jogging did Rachel begin jogging?
2 minutes
How far did the ball move in the final 2 seconds?
6 m (3.0 m/s ´ 2 s = 6 m)
What is Kathy's average speed?
Average speed = distance/time = 1,500 m/10 min = 150 m/min
Which of these is an example of deceleration? A. a bird taking off for flight B. a roller coaster moving down a steep hill C. a car approaching a red light D. an airplane following a straight flight path
C. a car approaching a red light
Wind-up toy car A starts moving in one direction. After 1 unit of time, toy car B starts moving in the same direction and car A has traveled 5 cm. If, on a distance-versus-time graph, the two straight lines that represent their motions cross, which wind-up toy car is traveling faster? Explain. (2)
Car B is traveling faster. At the point where the two lines cross, car B and car A have traveled the same distance. Because car A started before car B, car B had to cover that distance in less time than car A. Therefore, car B has to be traveling faster.
In an acceleration graph showing speed versus time, a straight line shows the acceleration is
Constant
What two variables are plotted in the graph?
Distance and time
T OR F A STRAIGHT line on a graph of speed-versus-time means that the object has a constant acceleration.
FALSE; Horizontal
T OR F AVERAGE SPEED is the rate at which an object is moving at a given instant
FALSE; Instantaneous speed
T OR F If a toy car traveling at 10 cm/s passes a toy car moving at 10 cm/s in the opposite direction, both cars have the same VELOCITY
FALSE; Speed
You are in a speed boat on a river moving in the same direction as the current. The speedometer on the boat shows that its speed is 20 km/h. However, a person on the shore measures the boat's speed as 23 km/h. How is this possible? (4)
From the reference point of the river, the speed of the boat is 20 km/h. From the reference point of someone standing on the shore, the speed of the boat is the speed on the speedometer plus the downstream speed of the current.
A speed of 15 kilometers per hour is abbreviated as 15 ______
Km/h
Does the graph indicate that the ball decelerated? Explain your answer.
No. Deceleration is a negative acceleration, which means an object slows down. According to the graph, the ball's velocity increased in the first three seconds and then remained the same for the next 2 seconds. It did not slow down. A line that slopes downward would indicate deceleration.
Describe Rachel's motion at 9 minutes.
Rachel is not moving; she is at rest or stationary
Suppose you are sitting in a car at a red light when a car moving toward the north begins to pass you. If you use the passing car as a reference point, the direction in which you appear to be moving is toward the ___________________.
South
Acceleration is the rate of change in _________
Speed
The distance traveled by a moving object per unit of time is called
Speed
A reference point is assumed to be ____________________, or not moving
Stationary
T OR F A straight diagonal line on a DISTANCE-VERSUS-TIME graph indicates constant speed.
TRUE
T OR F Motion is measured relative to a REFERENCE POINT
TRUE
T OR F A child riding on a merry-go-round is accelerating because his direction is CHANGING.
TRUE;
People living at Earth's equator are traveling at a speed of about 1,670 km/h as Earth spins on its axis. Are these people being accelerated? Explain. (1, 1)
They are being accelerated because the direction of their motion is constantly changing as they spin in a circle.
To determine the acceleration rate of an object, you must calculate the change in speed during each unit of
Time
You can show the motion of an object on a line graph in which you plot distance against
Time
A roller coaster is moving at 10 m/s at the top of a hill and 22 m/s at the bottom of the hill two seconds later. Explain how to find the average acceleration of the roller coaster, and then find the average acceleration.
To find average acceleration, divide the change in speed from the top of the hill to the bottom of the hill by the time it took the roller coaster to move from the top of the hill to the bottom of the hill.
Explain how to find the average speed of a car that travels 300 kilometers in 6 hours. Then find the average speed.
To find average speed, divide the distance traveled, 300 km, by the time to travel the distance, 6 h. Average speed = Distance/Time = 300 km/6 h = 50 km/h
Changing direction is an example of a kind of
acceleration
Speed that does not change is referred to as ____________speed
constant
If the speed of an object does NOT change, the object is traveling at a
constant speed
The moon accelerates because it is
continuously changing direction
When an object's distance from another object is changing,
it is in motion.
The abbreviation of the unit of acceleration (meters per second per second) is ____________________.
m/s2
The motion of a car stopping at a traffic light is an example of a(n) ___________________ acceleration, also called deceleration
negative
On a graph showing distance versus time, a horizontal line represents an object that is
not moving at all
If two lines appear on the same motion graph, the line with the steeper ____________________ indicates a greater speed.
slope
If you know the distance an object has traveled in a certain amount of time, you can determine
the speed of the object
Average speed is
the total distance traveled divided by the total time.
Speed equals distance divided by
time
When you know both the speed and direction of an object's motion, you know the
velocity of the object
