Review and Note Packet: Forces and Newton’s Laws of Motion
Follow the links below, read the text on the page, follow the instructions given and answer the
questions as directed below directly on this worksheet (yes, you’ll type any answers you find during
class. You should then save this worksheet to your own USB drive and print it off at home (or continue
working with the digital copy)).
You will find all the necessary links to help you answer the questions on this note packet by going to
www.physicsrocks.com and looking at the assignment calendar for today’s date. You may find some
other useful links by navigating to the “WebLinks” page and looking at the Mechanics section. You
may also find it useful to use the purple textbooks in the classroom cabinet (but please return them!)
Your name: _______________________________ Date: ____________ Period:_______
Part 1: Newton’s 1st law of motion, Inertia, and Types of Forces
1.
In your own words, state Newton’s first law of motion:
2. In your own words, explain the concept of inertia:
3. Think back to the WebAssign problem related to the helium balloon. Describe specifically, and in
your own words, why the balloon behaves as stated in the problem.
4. Follow the link to the Section discussing the car and the wall. Read through the scenario on that
page. Explain, in your own words, what happens, and why?
5. Find good definitions for the following force types. In your own words, describe them, discuss how
they might be measured or determined, and state at least 2 acceptable abbreviations that could be
used in a free-body diagram:
a. Weight
b. Tension
c. Normal force
d. Friction
e. Air resistance
f.
Thrust
Part 2: Newton’s 2nd law and Equilibrium
6. What, specifically, is ALWAYS true about a system in equilibrium?
7. There are two distinct types of equilibrium in which a system may find itself. Clearly describe each,
noting any similarities and differences. Give an example for each situation:
Type
Dynamic Equilibrium
Translational Equilibrium
Description
Example(s)
8. Give at least one other term that is synonymous with Translational Equilibrium.
9. A flower pot is hanging from a rope that is attached to the ceiling of an enclosed patio. If the flower
pot has a mass of 7.50 kg, what is the tension in the rope? How do you know?
10. A 15.0 kg flower pot is hanging from 4 ropes, all evenly spaced and all the same length. What is the
tension in each of the ropes?
11. If a plant in a pot, m = 25.00 kg, was to be hung from the ceiling using wires that would break if they
have a tension greater than 100.0 N. What is the minimum number of wires, assuming they are all
placed evenly around the pot and are all the same length, that will be needed to safely hang the
potted plant?
12. Al, of “Big Al’s Pizza”, wants to hang a sign in the mall walkway outside his restaurant’s door using
only 2 ropes. If the sign has a mass of 15.25 kg, and if the ropes on both ends make an angle of
47.0º with the ceiling, what tension is felt in the ropes?
Big Al’s
Pizza
a) Draw a free-body diagram for these forces
b) Determine the weight of the sign
c) Determine the tension in the ropes
13. What will happen to the tension if the ropes are more horizontal? Why?
Part 3: Newton’s Second Law and Acceleration of Masses
14. In your own words, explain what Newton’s 2nd law of motion tells us.
15. State the mathematical expression associated with Newton’s 2nd Law of motion. What do each of the
variables mean? What are each variable’s units?
16. Explain the sensation you feel as you ride a fast-moving elevator from the ground floor to the top of
high-rise building and back down. When do you feel heaviest? Lightest?
a. Draw free-body diagrams to show the 2 forces acting on you if you are standing on a
bathroom scale while riding this elevator in the following scenarios:
i. At rest on the ground floor
ii. Just beginning the journey upward from the ground floor
iii. Traveling at a constant velocity during the middle of the ride
iv. At the top of your ride just as you begin to slow down to come to a stop
v. At the top floor, just as you begin your journey back down
vi. Traveling at a constant downward velocity
vii. Just as you are coming to a stop at the ground floor.
b. For each of the scenarios above, use a second color pen and draw in a vector showing the
direction of the acceleration felt in each case. If ever the acceleration is zero, use that color
to write a = 0 m·s-2.
c. For each of the scenarios above, use a third color to draw in and label the direction of the net
force (Fnet).
d. What is always true about the directions of the net force and the acceleration?
e. Is your weight ever changing as you ride on the elevator? What is happening to make you
feel heavier/lighter at various points in the ride?
17. In the section on the Physics Classroom for Newton’s 2nd law, there are some “Check your
Understanding” Questions. Answer these. Make notes here about any questions/confusion you
currently have that still needs to be addressed!
18. The Big Misconception—according to The Physics Classroom:
a. What is the big misconception? Write this down in your own words
b. Do you agree with Anna or Noah? Explain.
19. Free Fall and Air Resistance
Read this page on The Physics Classroom along with the two animations given
a. Do objects of different mass have the same weight on Earth?
b. If we neglect air resistance, why do two objects of different mass have the same acceleration
due to gravity?
c. If we take air resistance into account, why does a more massive object usually fall faster?
d. What does it mean to have terminal velocity? Use a FBD in your answer to explain this.
e. Sketch a graph of a falling object’s velocity as it falls through the air. Sketch a second graph
showing a second object, dropped from the same vertical position, falling through the same
air, but that has half the mass as the first object. Why do your graphs look different?
Sample problems:
20. The typical acceleration when a car crashes into a wall at 60.0 km/h is approximately -150.0 m·s-2.
Imagine a mother holding her young child, m=20.0 kg, with no seatbelt on the child.
a. What force would be needed in order for the mother to hold on to her child during that sudden
deceleration?
b. How much weight, in pounds, is this force equivalent to?
c. How likely would it be for this mother to successfully hang on to her child?
21. Two blocks are connected by a rope that is over a pulley. Both blocks hang from their end of the
rope. The pulley is free to move and is considered to be frictionless. Block A has a mass of 2.0 kg,
and Block B has a mass of 4.0 kg
a. Assuming the two blocks together are the “system”, what is the acceleration of the system?
b. What is the net force acting on each block?
c. What is the tension in the rope connecting the two blocks?