Free Body Force Diagrams
Net Force Calculations
Newton's 1st, 2nd & 3rd Laws
Friction
Miscellaneous
100
What force is always present in a free body diagram?
Force of gravity or weight (Fg)
100
You set your cruise control for 65 mph. What is the net force acting on your car?
0 N, it is traveling at a constant velocity so all forces cancel
100
State Newton's 3rd Law of Motion.
For every action, there is an equal and opposite reaction.
100
Which type of friction is always less?
Static or kinetic friction
Kinetic friction
100
A person with a weight of 120 lb is standing on a scale. What force is the scale exerting on the person?
120 lb up
200
A box is sliding across a rough floor at a constant velocity. What forces act on the box?
gravity, friction, normal
200
Calculate the net force and give the direction it is acting in.
11 N to the right
200
Which of Newton's laws explains why a golf ball's acceleration is less when you putt vs. tee off?
Newton's 2nd Law
a = F/m
same mass, but different force results in different acceleration
200
What is the approximate value of static friction based on the graph?
75 N
200
What is the unit for force?
Newton
300
The free body diagram depicted is for a car driving to the left that is coming to a stop. Identify each of the forces (C,E,D) in the diagram.
C = normal force
E = friction
D = gravity
300
Calculate the net force and give the direction the force is acting in.
6 N to the right
300
Which of Newton's laws explains why you wear your seat belt?
Newton's 1st Law of Motion = Law of Inertia. Objects at rest stay at rest and objects in motion stay in motion until an unbalanced force acts on them
300
Which of these would be an appropriate value for the coefficient of friction between tennis shoes and a wood floor?
a. 0.01
b. 0.5
c. 0.1
d. 0.95
0.95
There is a lot of friction between the 2 surfaces, therefore the coefficient of friction is close to 1
300
What is the formula used to calculate the coefficient of friction?
u = Ff / FN
400
Describe a situation that could have the following free body diagram.
The object is accelerating toward the right.
A car accelerating to the right.
400
Calculate the magnitude of the net force acting on the object.
42.7 N
400
A 2,000 kg car is pulling a 1,000 kg trailer. Calculate the acceleration of the car and trailer based on the given diagram.
a = F/m = 4,000/3,000
a = 1.33 m/s2
400
Give an approximate value for the kinetic friction based on the graph.
2.2 N
400
Name the correct unit for each of the following measurements:
1. acceleration
2. mass
3. Force
4. velocity
5. coefficient of friction
1. acceleration = m/s2
2. mass = kg
3. Force = N
4. velocity = m/s
5. coefficient of friction = unitless
500
Identify the missing values:
Fnet = _____
m = 50 kg
a = ______
Fnet = 750 N
m = 50 kg
a = 750 / 50 = 15 m/s2 right
Fg = (50)(10) = 500 N
FN = 500 N
500
Calculate the magnitude, angle, and direction of the net force acting on the object shown.
42.7 N @ 690 N of E
500
Tell which of Newton's Laws best applies to each scenario:
1.) A cannon recoils when you fire it
2.) Bunting vs. hitting a home run
3.) Pulling a tablecloth out from under a set of dishes
4.) As you step onto a dock from a boat, the boat moves backwards
5.) It takes longer to accelerate a semi than a motorcycle from a stopped position
1. Third Law
2. Second Law
3. First Law
4. Third Law
5. Second Law
500
If the frictional force is 50 N and the mass of an object is 10 kg, calculate the coefficient of friction between the 2 surfaces.
u = Ff/FN = 50 N/100 N = 0.5
FN = Fg = mg = (10)(10) = 100 N
500
Fill in the missing blanks:
Fnet = _______
m = ________
a = 4 m/s2 right
Fnet = 32 N
m = 8 kg
a = 4 m/s2 right
Fgrav = 80 N
Ffrict = 32 N
u = 0.4