The rate of change

of velocity

at a given time

interval

PositivePositive acceleration acceleration

ConstantConstant acceleration acceleration

Negative Negative accelerationacceleration

Problems:1. The velocity of a car increases from 2.0 m/s at 1.0 second to 16 m/s at 4.5 seconds. What is the car’s average acceleration?

2. Michael is driving his sports car at 30 m/s when he sees a dog on the road ahead. He slams on the brakes and comes to a stop in 3.0 seconds. What was the acceleration of Michael’s car?

3. A race car’s velocity increases from 4.0 m/s to 36m/s over a 4.0 s period. What is its average acceleration?

4. A bus is moving at 25m/s. The driver steps on the brakes, and the bus stops in 3.0 seconds. What is the average acceleration of the bus?

The three basic equations in description of motion in one dimension with constant acceleration are

1. v=d/t 3. a = vf – vi

t

2. v = vf+vi

2

Sample problems:

1. A train accelerates from 30 kph to 45 kph in 15.0 s.

Find it’s a. acceleration b. distance (m) it traveled during this time.

2. Albert is riding his scooter at a velocity of 80 kph when he sees an old woman crossing the road 45 m away.

He immediately steps hard on the brakes to get the maximum deceleration of 7.5 m/s2. How far will he go before stopping. Will he hit the old woman?

3. A driver traveling at 20 kph tries to stop the car and finds that the brakes have failed.

The emergency brake is then pulled and the car comes to a stop in 120 m. Find the car’s deceleration in m/s2?

4. A bicycle accelerates from rest at 0.016 m/s2.

How long did it take the bicycle to acquire a speed of 36 kph? Express your answer in minutes.

5. A car has an initial velocity of 40 m/s. It stops over a distance of 120m when the

brakes

are

applied.

How long does it take for the car to stop? What is the car’s deceleration?

6. A bus traveling 50 m/s is increasing its speed at the rate of 4m/s2.

a.Find the distance covered in 6 s.

b. if its speed is decreasing at the rate of 4 m/s2, find the distance covered in 6 s and the time it takes to come to rest.

7. A car has an acceleration of 1 m/s2 .What is the change in its velocity after every 3 seconds?

8. A car is running at a speed of 80 m/s.It is the decelerated at the rate of 10m/s.When will it stop?

9. When a car is running with a velocity of 50 m/s, it is given a constant acceleration of 5m/s2? Find the displacement of the car 2 s later?

10. A driver decelerates his car from a velocity of 60 kph and brings it to a stop in exactly 5 s.Find the deceleration.

11. A car running at a speed of 72 kph is to be stopped in exactly 10 s.Find the uniform deceleration needed.