Physical Science Ch 9 Motion

Speed is defined as the distance traveled per unit of time. Therefore, in order to calculate speed, one needs to divide the distance traveled by the time it took to cover that distance. This is why the correct answer is "time". Velocity, size, and motion are not directly related to the calculation of speed.

When an object's distance from another object is changing, it indicates that the object is in motion. Motion refers to the change in position of an object with respect to its surroundings over time. Therefore, the correct answer is "it is in motion."

The average speed of the bicyclist can be calculated by dividing the total distance traveled (30 kilometers) by the total time taken (2 hours). Therefore, 30 km / 2 hours = 15 km/h.

Acceleration is the correct answer because it refers to the rate at which velocity changes. Velocity is a vector quantity that includes both speed and direction, so when the velocity of an object changes, it means either the speed or the direction or both are changing. Acceleration specifically measures the change in velocity, whether it is an increase or decrease in speed, a change in direction, or a combination of both. Therefore, acceleration is the appropriate term to describe the rate at which velocity changes.

Deceleration refers to the decrease in speed or velocity of an object. In this case, a car approaching a red light is an example of deceleration because as the car gets closer to the red light, it slows down and eventually comes to a stop. The other options do not involve a decrease in speed. A bird taking off for flight involves an increase in speed, a roller coaster moving down a steep hill involves a constant or increasing speed, and an airplane following a straight path implies a constant speed as well.

The correct answer is "the total distance traveled divided by the total time." Average speed is calculated by dividing the total distance traveled by an object by the total time it takes to cover that distance. It gives an overall measure of how fast an object is moving on average, regardless of the direction it is moving in. This differs from velocity, which is a vector quantity that includes both speed and direction. The other options provided in the question are not accurate definitions of average speed.

A reference point is used as a standard for comparison to determine if something is in motion. It provides a fixed location or object that remains stationary while other objects or locations are observed for motion. By comparing the position or movement of other objects to the reference point, it can be determined if they are in motion or not.

In an acceleration graph showing speed versus time, a straight line indicates a constant acceleration. A straight line means that the speed is changing at a constant rate over time. If the line was increasing or decreasing, it would indicate that the acceleration is changing. Therefore, the correct answer is constant.

When you know both the speed and direction of an object's motion, you know the velocity of the object. Velocity is a vector quantity that includes both the magnitude (speed) and direction of an object's motion. So, knowing the speed and direction allows us to determine the velocity of the object.

Acceleration is the rate at which an object changes its velocity. When an object changes its direction, it is also changing its velocity, as velocity includes both speed and direction. Therefore, changing direction is an example of acceleration.

A horizontal line on a distance versus time graph signifies that the distance remains unchanged as time progresses. This indicates the object is stationary, meaning it is not moving at all. The other options suggest movement, but a horizontal line specifically shows no change in position.