Chapter 3

An object covers a distance of 8 meters in the first second of travel, another 8 meters during the next second, and 8 meters again during the third second. Its acceleration in meters per second per second is approximately 8. 0. 24. 5.

0

1.She moves at a constant speed in a constant direction. rephrase. 2. The speedometer of a car moving to the east reads 100 km/h. the car passes another car that is moving to west at 100 k/m. Do both cars have the same speed? Do they have the same velocity? 3. During a certain period of time, the speedometer of a car reads a constant 60 km/h. Does this indicate a constant speed? a constant velocity?

1. She moves at a constant velocity 2. Both cars have the same speed, but they have opposite velocities because they are moving in opposite directions 3. The speedometer reading indicates a constant speed but not a constant velocity, because the car may not be moving along a straight line path.

1. What is the average speed of a cheetah that sprints 100 meters in 4 second? IF it sprints 50m in 2s? 2. if a care moves with an average speed of 60 km/h for an hour, it will travel a distance of 60 k. a. how far would it travel if it moved at this rate for 4h? b. for 10h?

1. in both cases the answer is 25 m/s 2. a. 60km/h*4 h =240km b. 60km/h*10 h=600km

A horse gallops a distance of 10 kilometers in a time of 30 minutes. Its average speed is 30 km/h. 15 km/h. 20 km/h. 40 km/h.

20 km/h.

Velocity

An objects speed and direction of motion

vector quantity

a quantity that has both magnitude and direction

scalar quantity

a quantity that has only a magnitude not a direction

It is important to understand that acceleration is the rate

at which velocity changes itself

total distance covered=

average speed* time interval

Acceleration=

change of velocity/time interval

The two measurements necessary for calculating average speed are velocity and time. distance and acceleration. acceleration and time. distance and time.

distance and time

Speed=

distance/time

speed

how fast an object moves; the distance traveled per unit of time

How far an object falls is entirely different from

how fast it falls

At the objects highest point when it is changing its direction of motion from upward to downward

its instantaneous speed is 0. Then it starts downward just as if it had been dropped from rest at that height.

free fall

motion under the influence of gravity only

A hungry mosquito sees you resting in a hammock in a 3-m/s breeze. How fast and in what direction should the mosquito fly in order to hover above you for lunch

the mosquito should fly toward you into the breeze. When just above you it should fly at 3m/s in order to hover at rest. Unless its grip on your skin is strong enough after landing, it must continue flying at 3 m/s to keep from being blown off. thats why a breeze is an effective deterrent to mosquito bites.

During each second of fall

the objects gains a speed of 10 meters per second

acceleration

the rate at which velocity changes with time; the change in velocity may be in magnitude or direction or both

Instantaneous Speed

the speed at any instant

Average speed

the total distance traveled divided by the time of travel

Average Speed=

total distance covered/ time interval

When a rock thrown straight upwards gets to the exact top of its path, its velocity is zero and its acceleration is about 10 meters per second per second. velocity is zero and its acceleration is zero. none of these velocity is about 10 m/s and its acceleration is about 10 meters per second per second.

velocity is zero and its acceleration is about 10 meters per second per second.

We say that a body is accelerating

when its velocity is changing

A car maintains a constant velocity of 100 km/hr for 10 seconds. During this interval its acceleration is 110 km/hr. 10 km/hr. 1000 km/hr. zero.

zero