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Sierzega/Ferri: Linear Dynamics 11
Putting It All Together
1. The speed of an object changes, as shown
in the graph below. The mass of the object
is 5 kg.
a) Describe the object’s motion in words,
as fully as possible.
b) Determine the acceleration of the object
for each segment of the graph (hint:
slope!).
c) Determine the sum of the forces (ΣF)
exerted on the object for each segment
of the graph.
2. You are pulling a suitcase, exerting an upward force of 200 N on it. The mass of the suitcase
is 15 kg.
a) Sketch the situation. Circle your object of interest.
b) Find the force Earth exerts on the suitcase.
c) Draw a force diagram for the suitcase; make sure the lengths of the arrows represent the
magnitudes of the forces.
d) Use the force diagram to draw a motion diagram for the suitcase.
e) How do you know if the diagrams are consistent with each other?
f) What is the acceleration of the suitcase?
3. For the same situation in problem 2:
a) What is the force that the suitcase exerts on your hand?
b) For as many as you can, list and draw diagrams for the Newton’s 3rd Law pairs for this
interaction.
4. You continue lifting the suitcase, but now you are exerting an upward force of 147 N on it.
a) Draw a force diagram for the suitcase; make sure the lengths of the arrows represent the
magnitudes of the forces.
b) Use the force diagram to draw the motion diagram for the suitcase. Check that your
diagrams are consistent.
c) Find the acceleration of the suitcase.
Sierzega/Ferri: Linear Dynamics 11
5. Five force diagrams are shown below. Draw a matching motion diagram and write a number
statement that can represent the situation (make up your own numbers).
6. When a hammer hits a nail, it exerts a 100 N force on the nail.
a) Does the nail exert a smaller or larger force on the hammer, or does it exert no force at
all?
b) For as many as you can, list and draw diagrams for the Newton’s Third Law Pairs for this
interaction.
7. A person stands on a bathroom scale that reads 712 N (160 lbs). The scale is placed on an
elevator floor and the person stand on the scale.
a) What does the scale read at the beginning of the ride when the elevator accelerates up at
2.0 m/s2?
b) What does the scale read when the elevator continues to move up at a constant speed of
4.0 m/s?
c) What does the scale read at the end of the ride when the elevator slows down at a rate of
2.0 m/s2?
8. You throw a tennis ball upward. Draw a motion diagram for the ball when (a) it is still in
contact with your hand, about to leave it, (b) when it is moving up, (c) when it is at the top of
its flight, (d) when it is moving down, and (e) when you catch it. Ignore air resistance. Then
draw a force diagram for (a) – (e).
Sierzega/Ferri: Linear Dynamics 11
9. Some students are trying to move a heavy desk (50 kg) across the room. Diana pushes it
across the floor. There is also a -200 N friction force exerted by the floor on the desk. The
sum of the forces on the desk is 275 N.
a) Make a sketch of the situation.
b) Draw a force diagram for the desk. Draw a motion diagram.
c) Write a math statement that describes the force diagram.
d) How hard is Diana pushing?
e) Is the desk moving with a constant velocity or is it speeding up?
f) What will happen after a few seconds if Diane stops pushing?
10. You are pulling a wagon with some bricks on it exerting a force of 150 N over a rough
concrete surface. The wagon and bricks have a combined mass of 25 kg and the concrete
exerts a resistive force of 105 N.
a) Draw a motion diagram and force diagram for the situation.
b) What is the acceleration of the wagon?
c) If the wagon starts at rest, what is the velocity of the wagon after 5 seconds?
Useful Information
Equation
Variable
= final velocity
= acceleration
= time
= initial velocity
= final position
= average velocity
= time
= initial position
= force
= mass
= acceleration
= acceleration
= sum of the forces
= mass
Units
= m/s
= m/s2
=s
= m/s
=m
= m/s
=s
=m
=N
= kg
= 10 m/s2
= m/s2
=N
= kg