1a. define: reference point
a point against which position is measured
1b. define: vector quantity
a physical measurement that contains directional information
1c. define: scalar quantity
a physical measurement that does not contain directional information
1d. define: acceleration
the time rate of change of an objects velocity
1e. define: free fall
the motion of an object when it is falling solely under the influence of gravity
- If an objects position does not change relative to a reference point, is it in motion relative to that reference point?
it is not moving relative to the reference point
- A glass of water on the counter. Is it in motion?
the glass of water is moving relative to many reference points
- A child 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 of nor falling behind the other.
a. Relative to whom is the child in motion?
b. Relative to whom is the first girl in motion?
c. Relative to whom is the second girl not in motion?
a. the child is in motion relative to the two girls
b. the first girl is in motion relative to the child
c. the second girl is motionless relative to the first girl.
- What is the speed of a boat that travels 10 miles in 30 min? (answer in miles per hour)
20 miles per hour
- What is the speed of a jogger who jogs 6 kilometers in 45 minutes? (answer in meters per second)
2.2 meters per 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/second squared east
c. 3.4 feet/hour and slowing
d. 56 liters
e. 2.2miles/minute west
f. 2.2 millimeters/year
a. scalar-distance
b. vector-acceleration
c. scalar-speed
d. scalar-none of these
e. vector-velocity
f. scalar-speed
- 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 care, what is the relative velocity?
12 miles per hour towards each other
- If an object travels for 15 minutes with a constant velocity of 12 miles per hour west, what is the acceleration?
the acceleration is zero
- 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 m/sec squared east
- 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 takes 12 min to come to a stop, what is the trains acceleration?
150 miles/hour squared 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 restence 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 fall near the surface of the earth?
the effect of air resistance is so small on heavy objects that it can usually 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 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 frock to fall to the group. What is the balloonists altitude in feet?
784 feet
- A scientist decides to study the acceleration of an object moving in a straight line. He measures sthe 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 int the previous interval. Is the direction of the acceleration the same as or opposite of the velocity?
opposite direction
