A car is driven for 1.00 h with a velocity of 90 km/h towards the south, then for 0.50 h with a velocity of 45 km/h
towards the north, and finally for 0.45 h with a velocity of 65 km/h towards the south. Find the car’s average
velocity and its average speed. Express your answers in both km/h and in m/s
Answers
Explanation:
There is more to motion than distance and displacement. Questions such as, “How long does a foot race take?” and “What was the runner’s speed?” cannot be answered without an understanding of other concepts. In this section we add definitions of time, velocity, and speed to expand our description of motion.
Time
As discussed in Physical Quantities and Units, the most fundamental physical quantities are defined by how they are measured. This is the case with time. Every measurement of time involves measuring a change in some physical quantity. It may be a number on a digital clock, a heartbeat, or the position of the Sun in the sky. In physics, the definition of time is simple— time is change, or the interval over which change occurs. It is impossible to know that time has passed unless something changes.