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Balanced Force Particle Model:
Review Sheet
1. For each of the drawings below, draw a system schema labeling all the objects and forces
present. Then draw a free body diagram. If necessary, draw another diagram showing the
components of any forces. Be sure to include any equality marks if there are forces (or
components) that are equal
A.
5 kg
B.
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C. Draw a free-body diagram for each weight in this diagram.
D.
E.
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2. Referring back to the previous problem, use your knowledge of forces to calculate the values
for the given forces in those diagrams.
A. Determine the tension in the string.
B. Determine the tension in both strings.
C. Determine the tension in both strings.
D. If the person had a mass of 60 kg, determine the weight of the person. Without a full
calculation, determine if the value of the tension in the angled string is more or less than the
weight of the person
E. If the elephant had a mass of 1000 kg, determine the weight of the elephant. Assuming
the elephant is not moving, determine if the normal force acting on the elephant is larger or
smaller than the weight of the elephant.
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3. Consider a collision between a small car and a heavy truck. In such a collision, how does the
size of the force exerted on the car by the truck compare with the size of the force exerted on
the truck by the car? Explain your reasoning.
4. a. Draw a velocity-time graph for a ball
thrown vertically into the air during its
up-and-down motion.
b. Draw a force diagram for the thrown ball
when it reaches its highest point.
c. At the highest point, is the velocity zero? Explain.
d. At the highest point, is the acceleration zero? Explain.
e. At the highest point, is the net force zero (i.e. are the forces balanced)? Explain how you
know.
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5. You push a grocery cart along a level floor in the presence of friction effects
between the cart and the floor.
a. Draw force diagrams for you and the cart. Fully label all vectors.
you
cart
b. While you are making the cart speed up, how does the size of the force you apply on the
cart compare to the size of the force the cart exerts on you? Explain.
c. While you are making the cart speed up, how does the size of the frictional force on the
cart by the floor compare to the frictional force on you by the floor?
d. Identify all of the Newton’s Third Law pairs in your force diagrams.
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6. A 35 kg child pulls a 12 kg wagon up a hill at 0.6 m/s. The wagon exerts 60 N of force on the child.
a. Draw a quantitative force diagram for the wagon by drawing the force vectors to scale
and labeling the values of the forces that you can determine.
30°
b. Explain how you applied Newton’s first law to make the force diagram quantitative.
c. Explain how you applied Newton’s third law to make the force diagram quantitative.
7. You have invested in the next great fad: Spring Shoes! They are a set of spring that attach to
the bottom of your shoes to make you super bouncy.
a. Draw a free body diagram of the forces acting on a person wearing Spring Shoes.
b. If the person has a mass of 75 kg, determine the value of the spring force while the person is
at rest.
c. Assuming the springs compress a distance of 0.08 m, determine the value for the spring
constant for our Spring Shoes
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