# 1.1.2 Part 2 Chapter 11.3 Acceleration & Momentum

## 1.1.2 part 2 Chapter 11.3 Acceleration & Momentum

Acceleration - rate of change of velocity (usually m/s2) (p.342)

- Can occur through a change in
**speed or a change in direction or both** - Do you experience acceleration when your car goes around a curve?
- Do you experience acceleration when you ride a roller coaster?
- Do you experience acceleration when you ride a carousel?
- Acceleration due to gravity = 9.8 m/s2

Positive acceleration - increasing change in speed (i.e. first starting off at a stoplight) (p.347)

Negative acceleration - decreasing change in speed (i.e. slowing down at a stoplight) (p. 347)

Constant acceleration – the velocity of an object moving in a straight line that changes at a constant rate (p. 345)

Instantaneous acceleration – how fast a velocity is changing at a specific instant or moment (p. 348)

Constant speed and direction = zero acceleration

To calculate acceleration:

a = acceleration

vf = final velocity

vi = initial velocity

t = time

a = vf – vi

t

NOTE: You can have a positive or negative acceleration depending on if you are speeding up or slowing down.

**Graphs of Accelerated Motion (p. 356)**

- You need to know how to interpret acceleration graphically
- Speed is plotted on the y-axis (vertical) and time is plotted on the x-axis (horizontal)
- The slope of the line is the acceleration
- Slope = Rise

Run

- Refer to graphs on p. 347
- Horizontal parts of the graph = constant speed; acceleration = 0

Momentum – the product of an object’s mass and velocity

- i.e. an object has a large momentum if the product of its mass and velocity is large
- Which has a greater momentum === a toy fire truck or a real fire truck?
- Which has a greater momentum === a loaded shopping cart or a small glass marble?
- The momentum of an object at rest is zero.
- 100kg object moving 1m/s has the same momentum as a 1kg object moving 100m/s.
- Airbags, “follow-through” when you throw or shoot, bending knees when you land from a jump

Momentum = Mass x Velocity

Momentum is measured in kilogram-meters per second.

Conservation of Momentum – if no net force acts on a system, then the total momentum of the system does not change

- i.e. In a closed system, the loss of momentum of one object equals the gain in momentum of another object (momentum is conserved)

Samples:

1. What is the acceleration of a car that increases its velocity from 0 km/h to 100 km/h in 10 s?

2. What is the acceleration of a car that maintains a constant velocity of 100 km/h for 10 s?

3. What is the difference between negative and positive acceleration?

4. If a car was at rest, traveled north for 5.5s, and reached a final velocity of 22.0m/s, what was the car’s acceleration?

a. 4 m/s2b. 12.14 m/s2

c. 17.54 m/s2d. 27.5 4 m/s2

5. A watermelon is dropped from the roof of a very tall building. What is the best way to describe its acceleration from the time it is dropped until it hits the ground?

A. it can never reach 9.8 m/s2

b. It increases and then decreases after reaching 9.8 m/s2

c. It increases & then remains constant after reaching 9.8 m/s2

d. It increases after reaching 9.8 m/s2 .

6. At which letter or letters on the graph is there

zero acceleration?____

Positive acceleration?____

Negative acceleration?____

7. What is the acceleration of an object over a 4s period if its starting velocity is 8m/s and its final velocity if 20m/s?

8. If a meteoroid changed velocity from 1.0km/s to 1.8km/s in 0.03s, what is the acceleration of the meteoroid?

9. A skier traveling at 30.0 m/s falls and comes to rest 10.0s later. What is her average acceleration?

10. A speed boat navigates a straight path across a 5 mile section of the Pamlico River over a period of 25 minutes. On the return trip, the boater was forced to use a zigzag pattern to avoid crab pots; the return trip also takes 25 minutes. Which of the following is NOT true of the return trip?

A. the boater increased the displacement that he traveled on the return trip.

B. The boater increased his velocity on the return trip.

C. The boater increased his average speed on the return trip.

D. The boater increased his acceleration on the return trip.

11. The speed of an object increases 6m/s over 3s. What is its acceleration?

A. 2m/s2b. 3m/s2 c. 18m/s2 d. 0.5m/s2

12. The speed of an object increases 10 m/s over 10s. What is its acceleration?

A. 0 m/s2 b. 1 m/s2 c. 10 m/s2 d. 100 m/s2

13. How long does it take to accelerate an object from 10m/s to 18m/s if the acceleration over that period was 2 m/s2?

14. The speed of an object increases 12m/s over 3s. What is its acceleration?

15. Calculate the acceleration of a Boeing 747 flying at 150m/s and then slowing to 90m/s in 600s as it circles the airport.

16. Calculate the acceleration of a runner who speeds up from 4m/s to 6m/s in the last 10s of the race.

17. What is the acceleration of a car that travels 24m/s then comes to a stop in 8 seconds?

18. A boat leaves the dock and travels west reaching a velocity of 6m/s after 3s. What is its acceleration?

19. If a bicycle is decelerated from a velocity of 15m/s to a rest position in 25s, what is the average deceleration of the bicycle?

20. At the top of its highest hill, a roller coaster’s speed is 12m/s. 4s later it reaches a speed of 36m/s just before it reaches the bottom of the hill. What is the roller coater’s acceleration?