Name: _______________________________________
Core: _____________
STUDY GUIDE: MOTION AND FORCES UNIT
You should be able to explain how the motion of an object can be described by its position, direction of motion, and
speed with respect to some other object.
Position, Distance, and Displacement Practice Problems:
Use the number line to answer questions 1-3.
1. What is the position of each object?
Heart: -5
Cross: -2
Diamond: 3
2. What is the distance between the heart and the diamond? 8 meters
3. If the diamond moved to the heart’s position, and then to the cross’s position, what is its displacement? 5 meters
Use the number line below to answer to help answer questions 4-6. Freddy the cat started at the -3 meter position.
He then walked to other locations. Mark each new location with the letter for that part.
4. What was Freddy’s total distance traveled? 16 meters
5. What was Freddy’s total displacement? 2 meters
6. Why is Freddy’s total displacement and total distance traveled different?
The words “distance” and “displacement” mean different things. Distance refers to the total length of an object’s route
of travel. In Freddy’s case, he walked 2 meters, then 5 meters, then 1 meter, then 8 meters, so the total distance that he
traveled was 16 meters. Displacement refers to the difference between an object’s starting position and its ending
position. Freddy started at the position of -3 m and ended at the -5 m position. The difference between these two
points is 2 meters, so his total displacement is 2 meters.
Speed Practice Problems:
7. What is the equation for speed?
Speed = distance
time
8. How are speed and velocity different?
Velocity is the change in distance in a certain direction during a certain length of time. Velocity is a description of an
object’s speed and direction. Speed refers to the amount of distance traveled in a certain period of time. Unlike
speed, velocity is a vector, which means that it includes a magnitude (a number) and a direction. Speed only has a
magnitude, and does not include a direction. Therefore, speed is considered a scalar.
9. A car travels 300 km in 6 hours. What is the average speed of the car (in km/h)? Show your work.
300 km/ 6 hours = 50 km/h
10. What is the speed of a jet plane that flies 7200 km in 9 hours (in km/h)? Show your work.
7200 km / 9 hours = 800 km/h
11. A storm is moving toward your house at a speed of 20 km/h. It is now 60 km away from your house. How many
hours will it take the storm to reach your house if it continues to travel at this speed? Show your work.
If the storm moves at a speed of 20 km/h, then every hour it moves 20 km. If it is 60 km away from your house and
continues to move at that speed, then it will reach the house in 3 hours, because 60/20 = 30.
12. A swimmer can swim at a speed of 2.8 m/s in 6 minutes. What distance will she cover in that time? (Hint: How
many seconds are in a minute??) Show your work.
There are 60 seconds in a minute. 6 minutes x 60 seconds = 360 seconds. If she travels 2.8 meters every second,
then in 360 seconds, she travels 360 x 2.8. Her total distance traveled in 6 minutes (or 360 seconds) is 1008
meters.
13. What is the average speed of a walker who walk 500 m in 400 seconds? Show your work.
500 m/ 400 seconds  simplify the fraction  5 m/4 seconds  1.25 m/s
Velocity and Acceleration
14. What is acceleration?
Acceleration is the rate at which velocity changes. -Acceleration can result from a change in speed (increase or decrease),
a change in direction (back, forth, up, down, left, right), or changes in both. Like velocity, acceleration is also a vector
15. Which of the following scenarios show acceleration? B, C
a) A cyclist travels at a constant speed of 12 mph in a straight line.
b) A plane starts to slow down as it descends.
c) A runner changes direction.
d) A parked car.
16. Draw a speed-time graph showing acceleration from AB, deceleration from BC, and a constant speed from CD.
Label your axis and each point on the graph!
You should be able to explain the effects of balanced and unbalanced forces acting on an object (including friction,
gravity and magnets).
Balanced and Unbalanced Forces Practice Problems:
What kind of force (balanced or unbalanced) is acting on the object or objects in each of the scenarios below?
17.
18.
19.
20.
21.
22.
23.
A magnet is sitting on a table and there are no other objects around it. balanced
The north poles of two magnets are close enough to each other to repel. unbalanced
A soccer player kicks a ball. unbalanced
A chair is in a room. balanced
A boy trips on his way in to class. unbalanced
Two men push a crate in opposite directions with 50 N of force. balanced
Two men push a crate in the same direction with 100 N of force. unbalanced
What is the net force and the direction of movement in each scenario below?
24. Two tugboats are moving a barge. Tugboat Little John exerts a force of 3000N to the left. Tugboat Big Sue exerts a
force of 5000 N in the same direction.
Net force: 3000N + 5000N = 8000 N (added together, because they are going in the same direction)
Direction: To the left
25. Now suppose Tugboat Little John exerts a force of 2000 N pushing the barge left and Tugboat Big Sue exerts a force
of 500 N to the right.
Net force: 1500 N Direction: to the left
26. Both tugboats are exerting a force on the barge but the barge doesn’t move. What is the net force acting on the
barge? 0 N (balanced force)
Gravity Review Questions
27. As an object falls, its velocity changes at a rate of 9.8 m/s2. What is this an example of? acceleration
28. True or False: Regardless of the object’s mass, all objects fall at the same rate of acceleration due to gravity: True
29. True or False: The weight of an object affects how fast it falls: False
30. What is the total force of an object if it weighs 30 kg? (Hint: Refer to Newton’s 2nd Law of Motion).
Newton’s second law of motion explains the weight of objects. Weight is a measure of the force of gravity pulling on
an object of a given mass. The acceleration due to gravity of an object equals 9.8 m/s2, so if you know the mass of
an object, you can calculate its weight as:
F = mass x 9.8 m/s2.
Therefore, if the mass of the object is 30 kg and the acceleration due to gravity is 9.8 m/s2, then the force of the
object is 30 x 9.8 = 294 N.
Newton’s Laws Review Questions:
Each of the items below is represented by one of Newton’s Laws of Motion. Write a 1, 2, or 3 for each of the following to
indicate if it is Newton’s 1st Law, Newton’s 2nd Law, or Newton’s 3rd Law.
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44.
A climber pulls down on a rope causing his body to rise up along the rope. 3
Force = Mass x Acceleration. 2
Two bumper cars collide into each other and each car jolts backwards. 3
When you give your friend a lift on your bike you have to pedal harder and faster to keep the same speed (and
acceleration) as you had before you were on your bike alone. 2
For every action there is an equal and opposite reaction. 3
A smaller cannon ball leaves a cannon much faster than a heavier, larger cannon ball fired from the same cannon. 2
When you are standing in a subway train, and the train suddenly stops, your body continues to go forward. 1
An object at rest will stay at rest unless acted upon by an unbalanced force. 1
It is much easier to carry your backpack when it is empty rather than when it is full of books. 2
A boy is going down a slide. As he reaches the bottom, friction causes him to slow down and come to a stop. 1
As the wheels of a drag racing car smoke and spin backwards, they eventually begin to grip the race track and push
backwards on the road. In turn, the road reacts by pushing the wheels forward. 3
When you throw a bowling ball out of a canoe, the bowling ball moves forward and the canoe moves backward. 3
An object in motion tends to stay in motion unless acted upon by an unbalanced force. 1
A basketball sits in the ball cage in the gym. It remains motionless. 1
You should be able to illustrate the motion of an object using a graph to show a change in position over a period of
time.
Draw distance time graphs below for the following scenarios:
45. An object moves away from its initial position at a
constant speed.
46. A runner jogs at a constant pace, stops to check his
time, then runs back home.
You should also be able to Interpret distance versus time graphs for constant speed and variable motion. Interpret the
graph below and answer each question.
47. How many times did the object stop? 2 times
48. What is the object’s speed at 4 minutes?
2 miles/5 minutes = .4 miles/minute
49. Describe what is happening between minutes 6 to
10.
The object is returning to its initial starting
position, because the distance from 0 is
decreasing as time continues.
50. Create a story describing what is happening in the
graph. Be sure to express what time/minutes each
part of the story is.
Minute 0-5: Object is moving away from its initial position at a constant speed. Why?
Minute 5-6: Object stops. Why?
Minute 6-10: Object returns to its initial starting position at a constant speed. Why?
Minute 10-12: Object stops. Why?
Minute 12-20: Object continues to move away from home at a constant speed. Why?