Chapter 9: Motion

6. Greg is a jet pilot from the planet Xhyrgetcz. His jet will accelerate from rest to the speed of sound (343 m/s) in 4.375 seconds. What is the rate of acceleration for Greg's jet?

a = vf - vi / t a = 343-0 / 4.375 a = 78.4 m/s2

5. A dog is running through the park at 8 m/s while chasing a flying frisbee and realizes she is about to run into a tree. If she comes to a stop in 2 seconds to avoid hitting the tree, what is her rate of acceleration?

a = vi - vf / t a = 0 - 8 / 2 a = -8/2 a = -4m/s2

4. Lucy walks 5 km in 1.5 hours. She stops for an hour. She walks 1 km more in the next hour. What is her average speed?

average speed = total distance / total time 6 km / 3.5 hr. = 1.71km/hr²

Units for speed & distance (length):

speed = m/s ; the Si unit for distance is the meter

1. Joan jogs 4km at a speed of 3km/hr. How long does she jog for?

t = d/s 4km / 3km/hr = 1.33 hrs.

What is Motion?

when one object's distance from another object is changing in relation to a reference point

How is velocity different from speed? Describe how an object could change velocity, but not speed

-- Velocity includes the direction the object is traveling --An object can change velocity by changing direction but remains at the same speed.

How is speed calculated and what is the difference between average speed and instantaneous speed?

-- speed = distance / time -- average speed is the total distance divided by the total time - overall rate of speed instantaneous speed is speed at one instant in time - speedometer of a vehicle

what is acceleration? How can an object could change velocity, but no change speed

--The rate at which speed/velocity changes over time -- The speed, direction or both can change. If an object does not change speed, it can accelerate by changing direction.

3. Anne walks her dogs for 2000 meters and it takes 20 minutes. What is her speed in m/s? (Hint: convert minutes to seconds!)

20 min = 20 X 60 = 1200 sec. s = d/t s = 2000m / 1200 s = 1.67 m/s

2. Francis chases her kids for 30 minutes at a speed of 3km/hr. How far does she chase them? (Be sure to convert minutes into hours)

30 min. = .5 hr. d = s X t 3km/hr. X .5 hr. = 1.5 km

Relative motion: explain how 2 people viewing an object describe its motion differently?

Both people are using different reference points.