physical science chapter 4
A loaded garbage truck has low acceleration. It takes 10 seconds to go from 0km/h to 100km/h. What is the acceleration of the garbage truck?
the acceleration of the garbage is 100km/h/10 seconds or 10 km/h/s
how would it be possible for an object to be traveling with constant speed and still be accelerating?
the object would be moving in a curved path
coordinates
the origin of a graph are (0,0)
origin
the place where position equals zero
acceleration
the rate at which velocity changes
what is the speed of runner B at 100 seconds? Picture on page 103
the speed of the runner at 100 seconds would be 400m ÷ 100 seconds = 4m/s
constant speed
the speed that does not change over time
average speed
the total distance divided by the total time of a trip
independent variable
the variable usually represented on the x-axis of a graph
dependent variable
the variable usually represented on the y-axis of a grpah
you know time and distance and want to find the speed
v=d÷t
if you are given x-y axes coordinates of (4,9), which axis is represented by the number 9?
y-axis
you are traveling on the interstate highway at a speed of 65 mph. What is your speed in km/h? conversion factor is 1.0 mph = 1.6 km/h
65mph = 104km/h
free fall
an object accelerating under only the force of gravity
acceleration due to gravity
an object in free fall will accelerate toward Earth at 9.8m/s^2
postition
an object is given relative to an origin
projectile
an object moving in a curved path and affected only by gravity
For how many seconds has runner A run at the 300-meter position? picture on page 103
at the 300 meter runner ! has been running for 50 seconds
why is the position vs time graph for an object in free fall a curve?
since an object in free fall is acceleration due to gravity, the speed is changing at each point and slope is a measure of speed. A curved line indicates a changing slope.
velocity
speed with direction
you know the distance and speed and want to find the time
t=d÷v
a high-speed train travels at 300 km/h. How long (in hours) would it take the train to travel 1,500 km at this speed?
t=d÷v=1,500km ÷ 300 km/h = 5 hours
speed
distance divided by time
east
+
north
+
right
+
up
+
down
-
left
-
south
-
west
-
your starting place on a track is 30 centimeters. What is your new position if you move 10 centimeters to the left of this position?
20 centimeters
when a ball is first dropped off a cliff in free fall, it has an acceleration of 9.8m/s². What is its acceleration as it gets closer to the ground? Assume no air friction.
9.8m/s², because its acceleration is constant. Its speed changes, but acceleration stays constant.
how are the variables speed and velocity different? How are they similar?
Both speed and velocity can be calculated using the dame formula. However, velocity implies direction and speed whereas when reporting speed, it is not necessary to write a directions.
it takes brooke 10 minutes to run 1 mile. What is her speed in miles per minute?
Brooke's speed is 1 mile/minute
you do an experiment to find out how much light is needed to make house plants grow taller. The two variables in this experiment are the amount of light and the height of the plants. Which variable is the dependent variable and which is the independent?
The independent variable is light and the dependent variable is the height of the plants.
a pelican flies at a speed of 52 km/h for .25 hours. How many miles does the pelican travel?
[(52 km/h × .25h)] ÷ (1.6km/mi) x = 8.1 miles
graph
a mathematical diagram using two axes to represent the relationship between variables
vector
a variable that is decribed using both a number and a direction
you know speed and times and want to find the distance
d=v×t
Lance Armstrong's teammate, George Hincapie, averaged a speed of 33.6 km/h in the 15th stage of the Tour de France, which took 4.00 hours. How far (in kilometers) did he travel in the race?
d=v×t= (33.6 km/h)(4.oo h) =134km
Which of the graphs below shows an object that has stopped?
graph B on page 103 shows a picture of a graph with the slope of zero. It is a horizontal line
x-axis
is horizontal on a graph
slope
is the ration of rise to run (rise over run)
name three common units for measuring speed
mph, kph, m/s, ft/s
if you walk 8 blocks north and then 3 blocks south from your home, what is your position compared to your home?what distance did you walk?
my position is 5 blocks north of my house. I traveled a total of 11 blocks.
can an object have a speed of zero while it has an acceleration that is not zero?
yes, an object can have a speed of zero white it has a nonzero acceleration. For examples, when you toss a ball up and then catch it, its acceleration at every point is 9.8 m/sec2, but at the very top of its path, it is at rest with a speed of zero for an instant
What is the speed of an object that is standing still?
zero
