A girl travels 20 miles on her bicycle. The trip takes 2
hours. Express her speed in miles/hr.
 First,
we identify the variables in our problem:

distance (d) = 20 miles


time (t) = 2 hours

 We
place the variables in their correct position in the speed formula

S = d/t


S = 20 mi/2 hour

 Perform
the calculation and express the resulting speed value with the appropriate
unit:

S = 10 mi/hr

A car starts from a stoplight and is traveling with a velocity of
10 m/sec east in 20 seconds. What is the acceleration of the car?
 First
we identify the information that we are given in the problem:

v_{f}  10 m/sec


v_{o}  0 m/sec


time  20 seconds

 Then
we insert the given information into the acceleration formula:

a = (v_{f}  v_{o})/t


a = (10 m/sec  0 m/sec)/20 sec

 Solving
the problem gives an acceleration value of 0.5 m/sec^{2}.
Now try on
your own:
1. What is the speed of a rocket that travels 9000 meters in 12.12
seconds? 742.57 m/s
2. What is the speed of a jet plane that travels 528 meters in 4
seconds? 132 m/s
3. How long will your trip take (in hours) if you travel 350 km at
an average speed of 80 km/hr? 4.38 h
4. How far (in meters) will you travel in 3 minutes running at a
rate of 6 m/s? 1,080 m
5. A trip to Cape Canaveral, Florida takes 10 hours. The distance
is 816 km. Calculate
the average speed. 81.6 km/h
6. How many seconds will it take for a satellite to travel 450 km
at a rate of 120 m/s? 3,750 s
7. What is the speed of a walking person in m/s if the person
travels 1000 m in 20 minutes? 0.80 m/s
8. A ball rolls down a ramp for 15 seconds. If the initial
velocity of the ball was 0.8 m/sec and the
final
velocity was 7 m/sec, what was the acceleration of the ball ? 0.413 m/s²
9. A meteoroid changed velocity from 1.0 km/s to 1.8 km/s in 0.03
seconds. What is the acceleration of
the
meteoroid? 26.7 km/ s²
10. A car going 50mph accelerates to pass a truck. Five seconds
later the car is going 80mph. Calculate
the
acceleration of the car. 6 mph/s
11. The space shuttle releases a space telescope into orbit around
the earth. The telescope goes from
being
stationary to traveling at a speed of 1700 m/s in 25 seconds. What is the
acceleration of
the
satellite? 68 m/s²
12. A ball is rolled at a velocity of 12 m/sec. After 36
seconds, it comes to a stop. What is the
acceleration
of the ball? 0.33 m/s²
13. How much
force is needed to accelerate a truck with a mass of 2,000 kg, at a rate of 3
m/s²? 6,000 N
14. A dragster in a race accelerated from stop to 60 m/s by the
time it reached the finish line. The
dragster
moved in a straight line and traveled from the starting line to the finish line
in 8.0
sec. What was
the acceleration of the dragster? 7.5 m/s²
15. A 300 N force acts on a 25 kg object. The acceleration of the
object is 12 m/s²
Know ALSO the following vocabulary terms:
Constant speed – Speed that does not change
Velocity – Speed in a given direction
Frame of reference – A background used to judge motion or speed
Instantaneous Speed – Speed at a given moment in time
Speed – amount of distance traveled in a certain amount of time
Average Speed – total distance divided by total time
TimeDistance Graph – graph that shows speed of an object
Acceleration – change in velocity over time
Motion – an object changing position or distance in time
Rate of Change – amount of time it takes to change position or
motion
Inertia  tendency of a still object to stay still or miving
object to keep moving unless acted on by an unbalanced force
Force – push or pull
Centripetal Force – force keeping objects moving in a circle
Gravity – pull of objects in the universe – pull determined by mass
and distance
Newton’s Three Laws of Motion – 1^{st}: Law of Inertia
(see Inertia definition); 2nd: Force=mass x acceleration;
3^{rd}: For every action, there is an opposite and equal
reaction