Question

3.1 motion is relative

1. as you read this in your chair, how fast are you moving relative to the chair? relative to the sun?

3.2 speed

1. what two units of measurement are necessary for describing speed?
2. what kind of speed is registered by an automobile speedometer: average speed or instantaneous speed?
3. what is the average speed in kilometers per hour of a horse that gallops a distance of 15 km in a time of 30 minutes?
4. how far does a horse travel if it gallops at an average speed of 25 km/h for 30 minutes?

Explanation:

Question 1

Relative to the chair, since your position relative to the chair doesn't change (you're at rest with respect to the chair), your speed is 0 (because speed is the rate of change of position, and if position doesn't change, the change in position $\Delta x = 0$, so speed $v=\frac{\Delta x}{\Delta t}=0$). Relative to the Sun, the Earth is moving around the Sun, and you are on Earth. The Earth's orbital speed around the Sun is about 107,000 km/h (or you can also consider the rotational speed of the Earth, but the orbital speed is a major component here). So you are moving at approximately the Earth's orbital speed relative to the Sun (since you are part of the Earth - Sun system's motion).

Speed is defined as the distance traveled divided by the time taken, i.e., $v = \frac{d}{t}$. So we need a unit to measure distance (such as meters, kilometers, miles, etc.) and a unit to measure time (such as seconds, minutes, hours, etc.). For example, in the SI system, the unit of distance is the meter (m) and the unit of time is the second (s), so speed can be in m/s. In everyday use, we might use kilometers (km) for distance and hours (h) for time, giving speed in km/h.

Average speed is the total distance traveled divided by the total time taken over a period of time. Instantaneous speed is the speed at a particular instant in time. An automobile speedometer shows the speed of the car at the exact moment you look at it. For example, if you press the accelerator, the speedometer reading changes immediately to show the current speed, not an average over a longer time. So it registers instantaneous speed.

Answer:

Relative to the chair: 0 (speed units like m/s, km/h etc., but magnitude is 0). Relative to the Sun: Approximately 107,000 km/h (due to Earth's orbital motion around the Sun).

Question 2