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