1.
A car travels round a circular track at a constant speed of 40 km/h. Explain why the car’s velocity is not constant
Velocity is a vector quantity that depends on both direction and magnitude.
Since the car’s direction changes continuously as it travels around a circular track, its velocity changes all the time.
Is the car accelerating? Explain your answer.
Acceleration is defined as the rate of change of velocity with time.
Since velocity is changing, the car is accelerating.
2.
An athlete initially at rest, runs a 100 m race and completed it with an average speed of 13.2 m/s. Explain why at some point in time his instantaneous speed must have exceeded the average value.
Since the athlete starts from rest, he must have had a speed of less than 13.2 m/s during his acceleration.
Therefore, his speed at other parts of the race must exceed 13.2 m/sin order for the average to be obtained as 13.2 m/s