# Velocity and Average Acceleration

Worked Example

A cheetah running at 20 m s−1 slows down as it approaches a stream. Within 3.0s, its speed has reduced to 2 m s−1. Calculate the average acceleration of the cheetah.

Solve the following:

1. A sports car, accelerating from rest, was timed over 400 m and was found to reach a speed of 120 km h−1 in 18.0 s. a. What was the average speed of the car in m s−1?

b. Calculate the average acceleration of the car in km h−1 s−1.

c. What was its average acceleration in m s−2?

d. If the driver of the car had a reaction time of 0.60s, how far would the car travel while the driver was reacting to apply the brakes at this speed of 120 km h−1?

2. A bus travelling north along a straight road at 60 km h−1 slows down uniformly and takes 5.0s to stop. a. Calculate the magnitude of its acceleration in km h−1 s−1.

b. Calculate its acceleration in m s−2.

3. A Prius hybrid car starts from rest and accelerates uniformly for 8.0s. It reaches a final speed of 16 m s−1. a. What is the acceleration of the Prius?

b. What is the average velocity of the Prius?

c. Calculate the distance travelled by the Prius.

4. A new model Subaru can start from rest and travel 400 m in 16 s. a. What is its average acceleration during this time?

b. Calculate the final speed of the car.

c. What is its final speed in km h−1?

5. During its launch phase, a space-rocket accelerates uniformly from rest to 160 m s−1 in 4.0 s, then travels with a constant speed of 160 m s−1 for the next 5.0s. a. Calculate the initial acceleration of the rocket.

b. How far does the rocket travel in this 9s period?

c. What is the final speed of the rocket in km h−1?

d. What is the average speed of the rocket during the first 4.0s?

e. What is the average speed of the rocket during the 9.0s motion?

6. A diver plunges headfirst into a diving pool while...

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