Name: ________________________
Date: ______________ Period: ____
Mrs. SooHoo/Mr. Hueston
PHYSICS: Dynamics Study Guide
Dynamics Unit Test Topics
1. Force Diagrams
a. Able to draw a correct and accurate force diagram for an object of interest with
proper labels.
b. Able to determine whether a force diagram and a motion diagram are consistent.
2. Newton’s 1st Law
a. Definition: For an particular object of interest (the system), if no other objects
interact with the system object or if the sum of all the external forces exerted on
the system is zero (forces in the y direction are balanced and forces in the x
direction are balanced), then the system object continues moving at constant
velocity (including remaining at rest) as seen by observers in the inertial reference
frames.
b. Have a conceptual understanding of Newton’s 1st Law.
c. Able to apply Newton’s 1st Law to analyze the motion of an object.
3. Newton’s 2nd Law
a. Definition: a = ΣF/m
b. Have a conceptual understanding of Newton’s 2nd Law.
c. Able to apply Newton’s 2nd Law to analyze the motion of an object.
d. Able to apply Newton’s 2nd Law quantitatively (mathematically) to determine
unknown quantities (acceleration, mass, or a force exerted on the object of
interest).
4. Newton’s 3rd Law
a. Definition: When two objects interact, object 1 exerts a force on object 2. Object
2 in turn exerts an equal-magnitude, oppositely directed force on object 1:
F1on2 = -F2on1. Each force is caused by one object and is exerted on another object.
Since these two forces are exerted on two different objects, they cannot be added
to find a net force. These forces are called Newton’s 3rd Law force pairs.
b. Have a conceptual understanding of Newton’s 3rd Law.
c. Able to apply Newton’s 3rd Law to analyze the motion of an object.
5. Friction
a. Able to include friction in a force diagram for an object of interest.
b. Able to explain the difference between static friction and kinetic friction.
c. Able to quantitatively (mathematically) determine the force of friction, the normal
force, and the coefficient of friction (both static and kinetic).
Force Diagrams
Question 1: Draw a correct and properly labeled force diagram for the following scenario:
Lebron James is about to shoot a 3kg basketball to try and score the game winning basket with a
force of 5N. However, while the ball is still in his Andrew Bynum goes up and blocks the shot
with a force of 10N.
Question 2: Examine the following, unlabeled force diagram. [Hint: for the force that is on a
diagonal, break it up into its x and y components. See text book if unsure of how to do this.]
a.
b.
c.
d.
e.
Describe a situation that can be represented by the force diagram.
Label the forces in the diagram according to the situation you specified.
In which direction does the object in your scenario accelerate? Explain.
In which direction does the object in your scenario move? Explain.
Draw a motion diagram for the scenario you described in part a and explain whether the
force diagram is consistent with your motion diagram.
Newton’s 1st Law
Question 3: The following system of equations describes forces exerted on an object in the
vertical and in the horizontal direction. Describe two different situations that this system can
describe in which the object of interest is moving in two different directions:
x direction: 12.0 N +(- 9.0 N) = 3.0 N
y direction: 20.0 N +(-20.0 N) = 0
Question 4: Give an explanation for the following scenario using Newton’s 1st Law. To dislodge
ketchup from the bottom of a ketchup bottle, it is often turned upside down and thrusted
downward at high speeds and then abruptly halted.
Question 5: Answer the following questions:
a. If you slide a hockey puck across a frictionless patch of ice, there must be a horizontal
force on it to keep it in motion.
b. The reason a penny thrown straight up inside a bus will come back to your hand it that
you, the bus, the air inside the bus, and the penny are all moving at the same velocity.
c. There is a friction force of 10N between a box and a table top. In order to move the box
at constant velocity, you would have to supply a force: a) slightly less than 10N; b) No
force is required to move the box; c) slight greater than 10N; d) of 10N; e) cannot tell
from the information provided.
Newton’s 2nd Law
Question 6: Mario is accelerating his little red wagon at 6m/s2 when Wario throws a sandbag into
the wagon, effectively doubling its mass. If Mario continues to pull with the same force, the
acceleration of the wagon will become _______m/s2.
Question 7: The force needed to accelerate a 3kg physics book from rest with an acceleration of
4m/s2 is _______N. Draw a force diagram for this situation.
Question 8: The Moving Works shipping company can ship containers with a mass of 30,400 kg.
In order to transfer the containers from the ship to the loading dock, the containers are attached
to a heavy-duty cable and then lifted and moved using a crane.
a. The container is being lowered on the loading dock. It is slowing down to a stop as it
approaches the dock. Draw a force diagram and motion diagram for the container.
b. Are your diagrams consistent? Explain.
c. The maximum upward force the cable can exert on any one container is 309,000 N. What
is the maximum magnitude of the acceleration of the container? What is the direction of
the acceleration?
Question 9: A 10kg object is moving at a constant velocity of 5m/s. Suddenly a force is exerted
on the object and it comes to a rest. If it takes 1.2s for the object to come to rest, what is the force
needed for this situation to occur.
Newton’s 3rd Law
Question 10: True or False. A bicycle and a parked car have a head-on collision. The force
exerted on bicycle by the car is greater than the force exerted on the car by the bicycle. Explain
your reasoning.
Question 11: An unfortunate bug splatters against the windshield of a moving car. Compared to
the acceleration of the car, the acceleration of the bug is: a) the same; b) larger; c) smaller.
Explain.
Question 12: Two people pull on a rope in a tug-of-war. Each pulls with 100N of force. The
tension in the rope is: a) 0N; b) 50N; c) 100N; d) 200N; e) different at different points in the
rope. Explain your answer.
Friction
Question 13: What is the difference between static friction and kinetic friction? Give an example
of both.
Question 14: You push a 20 kg lawn mower to the right, exerting a 100 N force on it. You push
the lawn mower horizontally. The effective coefficient of kinetic friction between the grass and
mower is 0.60. Assume that g = 10 N/kg. Problem includes friction.
a) Draw a force diagram for the lawn mower.
b) Determine the acceleration of the lawn mower.
c) In which direction does the lawn mower move? How do you know?
Question 15: A car is driving along an icy road. The maximum coefficient of static friction
between the car and the road is 0.2. Represent the situation with a force and motion diagram.
Write Newton’s second law in component form. Determine everything you can about the
situation.