Reference point
A point against which position is measured.
Vector quantity
A physical measurement that contains directional information.
Scalar quantity
A physical measurement that does not contain directional information.
Acceleration
The time rate of change of an object's velocity.
Free fall
The motion of an object when it is falling solely under the influence of gravity.
If an object's position does not change relative to a reference point, is it in motion relative to that reference point?
No.
A glass of water sits on a counter. Is it in motion?
it is in motion relative to many reference points.
A child is floating in an inner tube on a still lake. His position does not change relative to a tree on the shore. He watches two girls jog along the shore of the lake. The girls are keeping perfect pace with each other. Neither is pulling ahead nor fall
a. The girls.
b. The child.
c. The first girl.
What is the speed of a boat that travels 10 miles in 30 minutes? Please answer in miles per hour.
0.5 miles/hour
What is the speed of a jogger who jogs 6 kilometers in 45 minutes? Please answer in meters per second.
2.2 meters/second
Label each quantity as a Vector or Scalar quantity. Also, identify it as speed, distance, velocity, acceleration, or none of these.
a. 10 meters
b. 1.2 meters/second2 east
c. 3.4 feet/hour and slowing
d. 56 liters
e. 2.2 miles/minute west
f. 2.2 millimete
a. distance- scalar
b. acceleration-vector
c. speed-scalar
d. none of these-scalar
e. velocity-vector
f. speed-scalar
A car and a truck are traveling north on a highway. The truck has a speed of 45 miles per hour and the car has a speed of 57 miles per hour. If the truck is ahead of the car, what is the relative velocity?
12 miles/hour
If an object travels for 15 minutes with a constant velocity of 12 miles per hour west, what is the acceleration?
Since the velocity is not changing, the acceleration is zero. The time was just put in there to fool you. Remember, acceleration is the change in velocity. With no change in velocity, there is no acceleration.
A sports car goes from a velocity of zero to a velocity of 12 meters per second east in 2 seconds. What is the cars acceleration?
6 meters/second2 east ( equation 9.2)
A train takes a long time to stop. That's what makes trains so dangerous to people who cross the tracks when one is near. If a train is traveling at 30 miles per hour south and it takes 12 minutes to come to a stop, what is the train's acceleration?
150 miles/hour2 north.
A very picky physicist states that it is impossible for any object to experience free fall near the earth's surface. Why is the physicist technically correct?
Air resistance is a second influence, and all objects experience air resistance.
Even though the physicist in question #12 is technically correct, why do we go ahead and assume that heavy objects are in free fall when they near the surface of the earth?
The effect of air resistance is so small on heavy objects that it usually can be ignored.
A long, vertical glass tube contains a feather and a penny. All the air is pumped out, and the tube is inverted, causing the penny and the feather to fall. Which hits the bottom of the tube first, the feather or the penny?
Neither will hit first. They both hit together.
What is the height of a building (in meters) if it takes a dropped rock 4.1 seconds to fall from its roof?
82.4 meters
A hot-air balloonist drops a rock from his balloon. It takes 7 seconds for the rock to fall to the ground. What is the balloonist's altitude in feet?
784 feet
A scientist decides to study the acceleration of an object moving in a straight line. He measures the distance the object travels in 30- second time intervals. The scientist notices that in each interval, the object travels a shorter distance than it did
Opposite.